Chapter 10: Experts

Expert witnesses provide scientific, technical, or other specialized knowledge that helps fact finders understand evidence and resolve issues — and this chapter extends the direct- and cross-examination strategies of Chapters 7 and 9 to the particular discovery stages, qualifications, and opinion-foundation requirements that experts demand.

Chapter 10

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10.1 Introduction

10.2 Expert Witnesses

A. Purposes of Expert Testimony

B. Qualifications of Experts

C. Areas of Expertise

10.3 The Law of Expert Testimony

A. Evidentiary Laws

B. Objections to Expert Testimony

10.4 Direct Examination of Expert Witnesses

A. Attorney Preparation

B. Witness Preparation

C. Qualifying the Expert

D. Planning Guide

E. Establishing Qualifications

F. Qualifying Resumes/Stipulations

G. Tendering the Expert

10.5 Expert Opinions

A. Opinions and Conclusions

B. Summary Expert Outline

C. Sources of Information

D. Hypothetical Questions

E. Narrative Responses

F. Explaining Specialized Terms

G. Treatises

10.6 Expert Cross-Examination

A. Preparing Cross-Examination

B. Cross-Examination Areas

C. Developing a Plan

10.7 Supportive and Discrediting Cross

A. Supportive Cross-Examination

B. Discrediting Cross-Examination

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REFLECTING ON ADVOCACY

Expert opinion . . . is only an ordinary guess in evening clothes.

—Hon. Curtis Bok in Kerstetter v. Commonwealth

The most common way people give up their power is by thinking they don’t have any.

—Alice Walker

Introduction

Expert witnesses provide decision makers and fact finders with evidence, explanations, and opinions to assist them in understanding and resolving relevant issues. They offer their expertise in simple cases and complicated cases in our increasingly complex world. Advocates rely on experts as counsel pursue and defend all types of cases.

Expert witnesses can testify when scientific, technical, or other specialized knowledge will assist the non-expert fact finder in understanding the evidence or determining a fact in issue. Expert testimony may be needed to explain, interpret, or apply the facts so a correct verdict, decision, or award can be rendered. Experts help parties win cases.

This Chapter covers experts who testify in trials, arbitrations, and administrative hearings. Many of the strategies, tactics, and techniques explained in Chapter 7 on direct examination and Chapter 9 on cross-examination regarding lay witnesses also apply to expert witnesses. The following sections explain additional approaches particularly applicable to experts. There are other types of experts (e.g., retained or consulting experts) that assist with pretrial and prehearing discovery who do not testify in a case and are not covered in this book.

In civil cases, pretrial discovery enables parties to know what the testifying experts think and will say. Discovery has produced prepared expert reports and/or the experts have been deposed. This process allows the lawyers to evaluate the expert opinions and may prompt a settlement.

Our justice system generally requires all witnesses to appear in person and give their testimony, unless an exceptional situation arises where they are unavailable. See § 3.6. In some jurisdictions in civil cases, it is common for busy experts to testify virtually because of their scheduling conflicts. Their expert testimony is presented through a video recording or, less often, through an audio or stenographically recorded transcript. Recorded testimony assures that the fact finders will hear or read the expert testimony, avoids problems with scheduling experts who have timing conflicts, and reduces overall expert costs.

Experts in civil cases may undergo two discovery/deposition stages. The first consists of a combination of disclosure and discovery methods including interrogatories, document production requests, and discovery depositions. These methods provide the opposing party with information about the expert, the expert’s opinions, and the bases of those opinions.

The second is a deposition taken to preserve testimony, taken because the expert may not be available to testify in person. The party who is presenting the expert witness conducts the direct examination of the expert followed by the opposing lawyer conducting cross-examination. The record of the deposition includes any objections, which are later decided with the recorded testimony edited to reflect the rulings. In cases where the expert will testify in person, there may a deposition taken for discovery but not taken to preserve examination testimony.

In criminal cases, both the prosecution and defense exchange information about expert opinions and testimony as required by applicable law and procedures, usually well before trial. The timing for this exchange may depend on which side has the burden of proof on an issue. These criminal case experts usually testify in person during the trial as required by constitutional and case law provisions. Their prospective testimony may also prompt plea bargaining.

Expert Witnesses

A. Purposes of Expert Testimony

Expert testimony serves several purposes. An expert may:

• Provide factual information. For example, a treating physician can testify to injuries suffered by a civil plaintiff.
• Apply expert knowledge to the facts of a case and render an opinion. For example, a project engineer can explain information about product design and testify to an opinion regarding its defects or lack of defects.
• Explain scientific principles and theories. For example, in a homicide case, a forensic pathologist can explain the medical principles involved in determining the cause of death.
• Introduce relevant evidence. For example, in a criminal case, an expert can explain the DNA results that prove or disprove a defendant’s involvement in a crime.
• Describe test procedures and results. For example, a chemist can explain testing procedures to identify drugs and describe the results, which prove the substance to be a drug.
• Explain real evidence introduced in the case. For example, a radiologist can explain the images produced by an MRI scan.
• Analyze the facts and provide an opinion regarding the likelihood of an event or occurrence. For example, an accident reconstruction expert may testify to likely causation.
• Calculate the amount of recoverable damages in a civil case. For example, an economist can testify to the present value of projected lost earnings of an injured plaintiff.
• *Render an opinion that contradicts the conclusions of an expert who testified for the opposing party. *For example, a prosecution psychiatrist can testify that a defendant was not mentally ill at the time the crime was committed, which contradicts the expert opinion of a defense psychiatrist.

B. Qualifications of Experts

A person who has scientific, technical, or other specialized knowledge gained by education, training, experience, or skill may be qualified as an expert. Professionals, such as doctors, engineers, and economists, who have had extensive formal education and training, may be readily qualified. Other individuals whose expertise has been derived primarily from experience or skill, such as mechanics and technicians, may also be qualified if they have the requisite background, training, and experience. The laws of a jurisdiction determine who may be an expert, as explained below and in Section 10.3.

C. Areas of Expertise

An area of knowledge that contains scientific, technical or other specialized knowledge constitutes an area of expertise allowing expert testimony. A general test concerning expert testimony that most jurisdictions apply is: whether the area of expertise has gained general acceptance within the relevant scientific, technical or other specialized expert community. A scientific or tech subject or specialized field which has gained general acceptance within the relevant expert community or which has been verified by reliable research or tests is ordinarily recognized as a proper expert topic. These fields of expertise include medicine, chemistry, engineering, economics, psychiatry, accounting, computer science, and law practice. Additional examples of recognized expert subjects include ballistics, mechanical repairs, property assessments, health exams, lab results, forensic analysis, data recovery, post-traumatic stress disorders, child abuse syndromes, and artificial intelligence.

Some areas may not ordinarily be recognized unless experts in the subject and related areas recognize and accept the subject as one reflecting specialized knowledge. These fields of expertise that are not widely accepted and require substantiated proof of reliability in a case include areas such as hypnosis and voice spectrograms. Other areas that are not traditionally considered areas of expertise or that are unusual may not be recognized as a subject of expertise. For example, individuals proficient in operating lie detectors are not generally considered experts because their opinions and lie detectors have not been recognized as accurate or reliable.

Judges, arbitrators, and administrative law judges (ALJs) commonly recognize or take judicial, arbitral, or administrative notice of the recognized field of expertise. An expert may need to be asked questions to establish reliability of the area: “How well recognized is this field of expertise? Do experts like you recognize this area as reliable and accurate?” The law of a jurisdiction determines the scope of acceptable expertise.

The Law of Expert Testimony

A. Evidentiary Laws

Every jurisdiction has specific laws regarding the qualifications of experts and recognized areas of expertise. The primary sources of the law are evidence rules and judicial decisions applying and interpreting the rules. In federal cases, Federal Rule of Evidence 702 and related rules and federal case law regulate expert testimony, including Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993), Kumho Tire Co v. Carmichael, 526 U.S. 137 (1999), and their progeny,

Federal courts rely on the federal rules and the U.S. Supreme Court case law standards, which establish factors to assess the admissibility of expert testimony. Some states rely on the principles previously established in Frye v. United States, 293 F. 1010 (D.C.Cir. 1923).

Fed. R. Evid. 702 codifies the Daubert/Kumho standards and states:

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent demonstrates to the court that it is more likely than not:

(a) The expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;

(b) The testimony is based on sufficient facts or data;

(c) The testimony is the product of reliable principles and methods; and

(d) The expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

The applicable expert provisions provide that judges, arbitrators, and ALJs are the gatekeepers** **to determine the admissibility of expert opinions. Fed. R. Evid. 702 clarifies that the proponent of the expert testimony has the burden of proving that the testimony meets the standard by a preponderance of the evidence. The rule further accentuates the requirement that the opinions of an expert are to be based on reliable applications of scientific methods and principles. The gatekeepers must find that it is more likely than not that an expert’s standards and methods are reliable and can be reliably applied to the facts in a case. The following factors help them determine the propriety of expert testimony.

An opinion by a qualified expert may be deemed reliable if the underlying theory, method, or technique:

• Is generally accepted by a relevant expert community;
• Has been subject to peer review or publication;
• Has been or can be tested or determined to be verifiable or irrefutable;
• Has an acceptable potential error rate;
• Is controlled by legitimate, recognized governing standards;

Is otherwise steadfastly reliable and reliably applied.

Additional factors that influence whether an opinion by a qualified expert is admissible include:

• If the expert’s inferences and opinions are adequately supported by the evidence;
• If the expert considered alternate explanations regarding outcomes or results and can explain why other explanations were rejected;
• If the expert applied a sufficient level of intellectual rigor in forming the opinion;
• If the field of expertise to which the expert belongs is known for reliable conclusions; and
• If the opinion was developed independently of the case or for the purpose of providing expert testimony.

A majority of states have adopted the federal approach. Some of these states have modified it by adding other factors, such as: the extent to which the standards rely on the subjective interpretation of the expert and the degree to which non-judicial uses have been made of the standards. For example, the use of economic information (e.g., dependable stock brokerage data) may be reliable for making major financial decisions and may be relied on by an expert in appropriate judicial cases.

About one quarter of state courts use the Frye test, also known as the “general acceptance test.” These jurisdictions broadly permit expert testimony on pertinent issues if the opinion to be offered is based on a principle that has gained general acceptance in the relevant expert field. The expert can testify whether an applicable principle has gained this general acceptance.

The remaining jurisdictions use a combination of the federal and Frye factors. State appellate court decisions and evidence rules explain the specific approach used. Arbitrators and administrative law judges commonly follow the expert evidence law applicable to the case in the same or similar way judicial judges apply the law.

B. Objections to Expert Testimony

Objections applicable to lay witnesses also apply to expert witnesses. See Chapter Four. The rules of evidence—and available objections—are more relaxed when applied to expert direct and cross examinations. The nature of the opinions and the experience many experts gain from being professional witnesses provide flexibility with the rules and procedures. Experts may testify to ultimate issues, for example. See Fed. R. Evid. 704. Objections should be made when strategically helpful and tactically useful.

Direct Examination

of Expert Witnesses

A. Attorney Preparation

The attorney should know the specific subject that the expert will testify about as well or better than the expert. Without this specialized information, the attorney may fail to recognize critical information or be unable to identify errors or discrepancies with the expert testimony. This failure will result in ineffective direct and cross-examinations.

There are a variety of ways lawyers can become well informed. They can become “experts” through studies, schooling, training, and learning. They can research topics through books, websites, treatises, articles, and Internet sources. They can also seek advice from colleagues and others who are knowledgeable about the area of expertise.

LLMs can provide helpful information relating to areas of expertise, and can identify potential expert witnesses, if the system is connected to trusted databases. In addition, LLMs can interpret an opposing expert’s testimony, providing potential weaknesses that a lawyer might exploit (and provide contradictory evidence). See §§ 1.1[C] & 1.10 [E].

The advocate may hire a consulting expert in the field to assist in this educational process. These retained experts will not be called to testify, and they serve to educate counsel and offer suggestions for direct examination of testifying experts and for the cross-examination of opposing experts. An expert may also serve as both a consulting expert and a testifying expert in appropriate situations, as, for example, to reduce costs. Some areas of expertise may have a limited number of potential experts or only a few experts may be available, requiring one expert to serve more than one role.

Further, lawyers can study videos and transcripts of previous cases in which an expert testified. This approach can help prepare an informed direct examination and can reveal areas of vulnerability for cross-examination. Counsel can also review recorded testimony from other individuals who are experts in the same or related areas and cases.

B. Witness Preparation

Expert witnesses need to be thoroughly prepared for their testimony. The approaches and guidelines explained in Section 7.4 for lay witness examinations are also applicable to experts, including the use of AI sources. There are additional considerations specifically related to experts that are covered in the subsequent sections of this Chapter.

Expert preparation can differ from lay witness preparation in several ways. It can be easier. The expert witness may have substantial experience testifying in cases, understanding how to be an effective witness and how to avoid being ineffectual. The expert knows the subject matter area very well and does not require as much substantive preparation. And the expert is a professional who has been selected in part because of the expert’s ability to communicate clearly and credibly.

There are likely to be some preparation challenges. The expert may be pompous and arrogant, and come across as egotistical or haughty. The professional witness may not accept directions from an advocate who may know less than the witness does. And the busy expert may not have the time or be willing to take enough time to prepare with the lawyer.

Whether it’s easy or challenging, it is crucial for the attorney to properly prepare an expert. Rehearsing direct and cross-examination is just as important for an expert as for a lay witness. Video recorded experts need to see and hear what they look and sound like on video. All experts need to be prepped on how they may win or lose a case by their attitude, appearance, and testimony.

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C. Qualifying the Expert

The rules of evidence require that the expert must be qualified in the area about which the expert will testify. See Fed. R. Evid. 702. The judge, arbitrator, or ALJ rules on whether an individual is “competent” and qualified to be an expert witness. This means that:

• The expert has education, training, experience or skill in a field beyond the knowledge of the fact finder;
• The scientific, technical, or other specialized knowledge of the expert will assist triers of fact to understand the evidence or to determine a fact in issue they cannot decide based on common knowledge; and
• The expert’s opinion is based on education, training, knowledge, experience or skill and not on speculation, conjecture, or unfounded conclusions.

The foundation necessary to qualify an expert is relatively straightforward and generally not difficult to prove if the expert has sufficient qualifications. Examples demonstrating the legal foundation for areas of expertise may be found in articles, books, treatises, AI resources, and websites on the subject of expert examinations, as well as from prior cases. After sufficient foundation has been laid to establish expert qualifications, the advocate may continue with questioning to elicit the expert opinion(s).

D. Planning Guide

The following is a summary guide for expert testimony preparation:

Name

Title

Personal Background

Community

Family

Hobbies

Clubs

Social organizations

Charitable organizations

How, When Expert Becomes Involved

Fact witness

Retained to testify

Examination of party or events

Neutral expert

Hired by plaintiff or defense

Fees

Occupation

Employer

Position/description/responsibilities

Prior employers/positions/responsibilities

Education

Undergraduate degrees

Institution

Graduation date

Advanced degrees

Institution

Graduation date

Training

What

Where

When

Sponsor

Certificates/licenses

Professional Organizations

Name

Purpose

Member/Position

Professional Achievements

Books

Articles

Websites

Blogs

Teaching

Presentations

Consultations with professionals

Awards/honors

Legal Experience

As Witness

Plaintiff or defense

Frequency of testifying

Consultant

Organization or parties

Frequency

Specialized Experience

Type of experience

Tests

Examinations

Study

Consulting

Research

AI systems/platforms

Specific Examinations or Tests Involved in Case

Type of expert work

Why

When

Where

How

Investigations/Interviews

Results

Reports

Date

Summary

Supplement

Opinions/Conclusions

Basis of Opinions

Sources of Conclusions

Report

Exhibits

LLM-backed sources

Other reliable information

Exhibits

Real and demonstrative evidence and visual aids

Exhibits already prepared

Exhibits to be prepared

Gen AI resources

Cross-Examination Areas

Weakness of profession/trade/specialty

Weakness of expertise/education/training

Weakness of opinion/conclusion

Insufficient factual bases

Sources of information not considered

Possible other explanations

Comparison to LLM-suggested data and outcomes

Bias/prejudice

Favorable or adverse interests

Lack of objective data

Lack of sufficient information

Lack of reasonable examinations/testing

Comparison with opposing experts

Conclusion of Examination

Final Point/Topic/Opinion

Last Question

E. Establishing Qualifications

Federal Rule of Evidence 705 permits experts to testify to an opinion and provide reasons for that conclusion without first testifying to the underlying facts or data. This Rule also provides the decision maker with the discretion to require the disclosure of fundamental information before the introduction of the opinion. The expert will likely be cross-examined regarding some of the underlying facts or data.

The evidence rules also recognize the significance of the introduction and presentation of expert qualifications. It’s important to explain the experience and talents of the expert. It’s vital that credentials be fully and timely introduced. It’s critical that fact finders understand and appreciate how qualifications support and bolster opinions and conclusions.

Because of the flexibility of Fed. R. Evid. 705 and similar state court rules, there are optional ways to establish the qualifications of an expert. This information may be presented at the beginning of the examination, or may be interspersed throughout the testimony and disclosed as experiences apply to a particular opinion. Whatever method or sequence is used to establish qualifications, an effort should be made to “personalize” the expert and demonstrate that the expert is very knowledgeable.

The expert’s education, work history, and personal background help humanize the expert. Some experts may sound arrogant when describing their background because in effect they are telling the fact finder how brilliant they are. Questions need to be designed and asked to establish how smart the expert is without resulting in boastful answers.

The following examples demonstrate two different ways of presenting an expert’s qualifications.

1. Qualifications at Beginning of Examination

It is traditional and may be easier to present the expert’s qualification in sequence at the beginning of the examination. Many judges, arbitrators, and ALJs are familiar with an expert examination presented in this way and are comfortable with this approach. However, this method may not be the most persuasive way of presenting the background of the witness. Lengthy qualifications presented at the beginning of the direct may bore the fact finder as tedious qualifications are presented in the abstract and may not appear to relate to forthcoming opinions and conclusions.

Example:

Lawyer: The plaintiff calls Dr. Rebecca Lee Crumpler.

Q: Dr. Crumpler, what kind of medical doctor are you?

Q: Do you live in our city?

Q: How long have you lived in our community?

Q: Do you have family?

Q: Where did you go to college?

Q: In what fields did you get your degree?

Q: Where did you go to medical school?

Q: When did you graduate from medical school?

Q: Where did you serve your internship?

Q: Where did you complete your residency?

Q: Did you specialize?

Q: Explain what that means.

Q: Are you board certified?

Q: What does that mean?

Q: What experience do you have in your specialty?

Q: Have you done any lecturing or teaching in your specialty or related areas?

Q: Have you written any books or articles or created any blogs or websites relating to your expertise or in related areas?

Q: Have you contributed to technological research platforms in your area of expertise?

Q: Do you belong to any professional organizations?

Q: Have you ever testified in court before?

Q: How often?

Q: Have you testified for both the plaintiff and the defense?

2. Qualifications During the Examination

A more effective way to explain the credentials of an expert may be to introduce them periodically during the examination to support relevant opinions. When qualifications are woven throughout the direct examination, the timely information and proffered opinion focus on specific issues. The advocate needs to orderly introduce the germane qualifications to buttress the pertinent conclusions.

Example:

Lawyer: Defendant calls Dr. Doug Ross as his expert witness.

Q: Where did you go to medical school?

Q: When did you graduate from medical school?

Q: What medical post-graduate training have you had?

Q: Did you train in a specialty?

Q: Explain your specialty.

Q: How long have you been practicing your specialty?

Q: Now, Doctor did you examine the knee of Mr. Baryshnikov?

Q: When was that?

Q: Where did the examination take place?

Q: How long did the examination last?

Q: Did you have sufficient time for the examination?

Q: Tell us what you did to perform the examination.

Q: While you were at medical school, what training did you have in conducting this kind of examination?

Q: Please describe how it specifically related to his knee injury.

Q: Have you had any further specialized training or education to treat injuries of the type that Mr. Baryshnikov has?

Q: Please explain.

Q: Was that training and experience helpful to you in diagnosing his acute injury?

Q: How?

Q: Have you ever lectured on the type of serious injury that Mr. Baryshnikov has suffered?

Q: What have you presented?

Q: Does your lecturing help you in diagnosing and treating injuries of this severity?

Q: Have you written any books or articles regarding that type of major injury?

Q: What have you authored?

Q: Do your publications assist you in your diagnosis and treatment of critical injuries of this kind?

Q: How so?

3. Early Introduction of Opinion and Qualifications

It may be preferable to introduce opinions early during an expert’s testimony, followed by a presentation of the specific qualifications for each opinion. As previously explained, Fed. R. Evid. 705 permits an expert to offer a conclusion without initially testifying to the underlying facts or data. The federal rules and state rules allow the prompt introduction of expert conclusions. This initial introduction directly connects the opinions with the expert’s background, education, credentials, experience, and work, making the testimony more applicable, timely, and impactful.

Example:

Q: Dr. Konrad Zuse, what doctorate degree do you have?

Q: What does this degree prepare you to do?

Q: Did you examine and analyze the HAL 9000 computer that is involved in this case?

Q: Describe your comprehensive examination and analysis.

Q: How long did your detailed examination and analysis take?

Q: Was that sufficient for a thorough examination and analysis?

Q: Describe the computer chip you carefully examined.

Q: Did you review in depth Patent 3,120,666 at issue in this case?

Q: Do you have an opinion whether the ILLIAC chip you examined violates that Patent?

Q: What is that expert opinion?

Q: Where did you learn how to properly analyze computer chips?

Q: At B.I.T., what advanced courses did you take that helped you learn how to analyze the ILLIAC computer chips?

Q: What relevant research did you conduct that assisted you in being able to analyze that type of computer chip?

Q: What blogs or websites did you author explaining the computer chip analysis method you used in this case?

F. Qualifying Resumes/Stipulations

An expert may also be qualified to testify by submission of the expert’s resume as an exhibit or through stipulations to the qualifications of the expert by opposing counsel. Judges, arbitrators, and ALJs may allow the curriculum vitae of the expert to be introduced as an exhibit in addition to oral testimony or in lieu of such testimony. If the case involves many experts, the attorneys may prefer, or the decision maker may require, the attorneys to submit complete or summary resumes instead of detailed qualification responses. This procedure shortens examinations, allowing the focus to be on the expert opinions and the bases of those opinions.

A lawyer may stipulate to the qualifications of an opponent’s expert, making it unnecessary for that expert to be qualified. Counsel may decide a stipulation is preferable to having oral testimony of the other side’s expert qualifications. This will be particularly true if the opponent’s expert has strong or better qualifications. Some judges, arbitrators, and ALJs may urge the attorneys to stipulate to each other’s experts to save time.

An advocate must consider whether the submission of resumes or the acceptance of a stipulation is tactically wise. It may be more effective for the fact finder to hear the expert testify to qualifications, especially if qualifications are impressive. A lawyer can refuse the offer of opposing counsel to stipulate and establish the qualifications through testimony.

In non-jury cases, discussions with the judge, arbitrator, or ALJ about the preferred ways to proceed with expert qualifications can be done before or during the trial or hearing. In jury trials, discussions with the judge about the use of resumes and offers of stipulations should be conducted outside the hearing of the jury to avoid improperly influencing the jurors with comments by the attorneys or rulings by the judge.

G. Tendering the Expert

Some jurisdictions require that the examining lawyer request the judge, arbitrator, or ALJ to accept the witness as an expert or “tender” the witness as an expert before continuing with the testimony: “Your Honor, we tender Dr. Watson as an expert forensic scientist.” The decision maker then decides whether the witness is qualified and permits the witness to proceed to testify as an expert. An opposing attorney could “pass/accept” the witness and not oppose the witness testifying as an expert.

In jury trials, unless counsel is completely certain the judge will accept the expert, the applicable motion should be made outside the hearing of the jury, in case the judge may decide the expert is not qualified. Neither the federal rules nor most state rules require the proffering lawyer to make this formal “tender” request. The process of tendering an expert must be followed in those jurisdictions that require such presentation.

Expert Opinions

A. Opinions and Conclusions

After a judge, arbitrator, or ALJ is convinced that a witness is qualified to give an expert opinion, the direct examiner must convince the fact finder that the expert is worth believing. Establishing this persuasive foundation requires counsel to present the information in a way that is accurate, understandable, authoritative, believable, and interesting. This will confirm that the opinion of this expert is reliable and convincing.

An expert will usually testify to several opinions. A case may involve a major and several subordinate or minor conclusions. Counsel may be required or prefer to use legal jargon as a predicate to the introduction of an opinion, such as to: “a reasonable degree of certainty.”

Example:

Q: Do you have an opinion based upon a reasonable degree of medical certainty?

A: Yes.

Q: What is that opinion, Dr. Hfuhrvhurr?

Example:

Q: Doctor, based on your expertise with fingerprint analysis and based on your examination of the fingerprints found on the sewing machine and your comparison of those fingerprints with the known fingerprints of the defendant, do you know whether the fingerprints found on the machine, Exhibit Six, are the defendant’s fingerprints?

A: Yes, I do.

Q: What is your expert conclusion, Dr. Evangelista Purkinje?

A: The fingerprints that were found on the sewing machine identically match the defendant’s left thumb and forefinger.

B. Summary Expert Outline

A summary outline of the direct examination of an expert ordinarily includes the following topics:

• The subject matter of the opinion,
• Principles that support the area of expertise and opinion,
• Sources of information relied upon by the expert,
• Standard tests or routine procedures used in the area,
• Specific tests or procedures used in the case,
• Other bases of the opinion of the expert,
• The opinion or conclusion, and
• An explanation of the opinion and conclusion.

C. Sources of Information

An expert witness must explain the sources of information or facts that support the opinion or conclusion. This information is critical to comply with the evidence rules and to convince the fact finder. The applicable evidence provisions commonly permit an expert to give an opinion without first having to provide the facts or data underlying the opinion. This approach permits flexibility regarding the order of the expert testimony. The expert may explain the sources either before or after rendering the conclusion, as previously explained in Section 10.4(E).

There are a variety of sources of information an expert may rely on:

• Personal, firsthand facts or data developed prior to the case.
• Information obtained from other experts, examinations, documents, tests, records, reports, witnesses, websites, technologically derived data (e.g., analytics, LLMs), and other relevant and reliable sources.
• Evidence including testimony heard by or told to the expert.
• Hypothetical questions.

Whatever information the expert relies upon, it must be of a type “reasonably relied upon” by experts in the same area of expertise in forming an opinion. See Fed. R. Evid. 703. This broad standard permits an expert to testify to any source of information, whether admissible or inadmissible as evidence, as long as experts reasonably rely upon this type of information.

1. Personal, Firsthand Information

An expert may have personal firsthand knowledge of information learned or perceived prior to the trial or hearing. The witness may testify to these sources after a proper foundation has been laid that includes the testing, analysis, observations or perceptions made, when and where these observations occurred, how the expert made these observations, who was present, and a description of the work performed.

Example:

Q: Fire Chief Molly Williams, were you at the scene of the fire?

A: Yes.

Q: When did you arrive at the scene?

A: We received the first alarm about ten minutes after the fire started, and I arrived at the casino about five minutes after we received the alarm.

Q: What did you see when you arrived at the casino building?

A: Flames were shooting out of all the windows on the west side of the building, and the walls on the east side had partially collapsed.

Q: What did you notice about the flames?

A: They were a very bright orange color and were spreading rapidly from north to south through the building.

Q: Who was at the scene of the fire when you arrived?

A: The owner of the casino, Samantha Jane Marquez.

Q: Did you talk with her?

A: Yes.

Q: What did she say?

A: She said, “It’s all good. The World Poker Tour is cancelled.” Then she sighed, whispering to herself, “Well done.”

An expert who has firsthand knowledge about physical evidence may need to testify to establish the appropriate chain of custody of evidence that may become an exhibit. Section 8.4(E) describes establishing the chain of custody. For example, an expert who examined and tested strands of hair recovered at the scene of a crime will testify to receiving a sealed container from a detective, opening the sealed container containing the hair, and resealing the container after the tests have been completed to demonstrate the hair that was tested is the same hair offered as relevant evidence.

Experts who examine or test an item of evidence may not be able to recall the specific exhibit. An expert who routinely handles and examines many physical objects may have no independent recollection of a specific exhibit. Notes made by the expert may be used to refresh recollection. Questions may be asked that first establish the regular or correct procedure used by the expert followed by questions that establish that those standard procedures were followed with the specific exhibit.

2. Information Obtained from Other Sources Prior to the Trial or Hearing

An expert may rely upon sources other than personal observations and experiences, as long as the type of information is relied upon by other experts in the same area to reach conclusions. This type of information may include evidence that is inadmissible at trial. The most common form of inadmissible evidence is hearsay. For example, in practice an expert may rely upon a hearsay statement, which the rules of evidence would exclude as unreliable in a legal case. If, however, experts ordinarily rely upon hearsay information in their work, the expert may rely upon hearsay in forming an opinion. The hearsay may derive from a person, document, social network communication, blog, chat forum, website, LLM, or other common source.

An expert may identify the underlying facts and data that helped form the basis of an opinion even if they are not admissible. Federal Rule of Evidence 703 permits an expert to describe the facts and data used in forming an opinion, even if the information is inadmissible. This Rule also allows the facts and data to be disclosed by the proponent if their probative value outweighs any prejudicial effect. Decision makers may permit an expert to testify that the expert relied upon information from sources that are inadmissible, and have discretion to permit the expert to explain the sources. This Rule recognizes that experts reliably rely on information in their areas of expertise that the formal rules of evidence deem unreliable.

Example:

Examining Lawyer:

Q: Have you had an opportunity to examine the plaintiff?

A: No. There was no need to.

Q: Dr. Who, what have you done to learn about the plaintiff’s medical condition?

A: I began by following proven, reliable protocols.

Q: How did you proceed?

A: I studied the entire health record of the plaintiff. I spoke with Dr. Harleen Frances Quinzel, and I read her medical reports. In addition, I’ve read the incident reports prepared by the Outdoor Emergency Medical Responders and I’ve read the statements given to the Alpine Ski Patrollers by the two eye witnesses.

Q: Did you rely on any scientific sources?

A: I viewed pertinent x-rays and MRI images taken of the

Plaintiff.

Q: And did you obtain other reliable information?

A: Yes. I reviewed relevant AI-enhanced data relating to the type of alleged injury.

Q: Is this the type of information that experts in the field of orthopedic surgery, like you, normally rely on to reach a conclusion or to form an opinion about a person’s injuries?

A: Yes, it certainly is.

Q: Based upon this information, and your experience, training, and education, do you have an opinion about the nature or type of injuries suffered by the plaintiff?

A: Yes, I do.

Q: What is that opinion?

A: I cannot find any evidence the plaintiff has suffered any permanent injury whatsoever.

3. Information Perceived or Made Known During the Case

An expert may base an opinion upon evidence introduced during the trial or hearing. The expert may obtain this evidence by sitting through the case, watching a video of the testimony, reading a transcript of the evidence, or by obtaining an accurate summary of this information. The substance of this evidence must also be the type of information that an expert in the same area relies upon to form an opinion.

Example:

Q: Dr. Jung, have you been here in court during the testimony of the defense psychiatrist, Dr. Jennifer Melfi?

A: Yes, the entire time.

Q: Have you had an opportunity to attend any other part of the trial?

A: No. It wasn’t necessary.

Q: Have you read any files or records concerning this trial?

A: Yes.

Q: What have you read?

A: I have read the complete court file including the expert reports in this case and the transcripts provided me by the court reporter of each day’s testimony.

Q: Is the type of information you received from listening to the defendant’s psychiatrist and from reading the daily transcripts of the testimony of all the other witnesses, the kind of information a forensic psychiatrist generally uses to form an opinion as to whether the defendant knew what she was doing or whether she knew what she did was wrong at the time she shot the security guard?

A: Yes, it is.

Q: Based upon this information and your education, training, and DSM experience, do you have an opinion whether the defendant knew what she was doing and if she knew it was wrong?

A: Yes, I do.

Q: What is that expert opinion?

A: My opinion is that the defendant knew exactly what she was doing when she shot the security guard and she knew it was wrong when she did it.

D. Hypothetical Questions

An expert may base an opinion upon a hypothetical question. The direct examiner asks the witness the hypothetical question that contains facts that have been or will be introduced during the trial or hearing. The expert, not having personal knowledge of these facts and not having heard these facts during the case, is asked to presume facts set out in the hypothetical question in forming an opinion. The Federal Rules of Evidence and similar state rules no longer require hypothetical questions to be used to introduce an opinion. Hypothetical questions are often unwieldly and less effective than relying on one of the previously explained sources of information upon which experts can rely.

If used, hypothetical questions should be prepared in advance with the help of the expert. They should be written out in order to avoid mistakes and should be accurate, complete, and as short as possible. The attorney should practice reading the question so that the question can be presented in an interesting way. Long, complicated hypothetical questions can be cumbersome and sound monotonous. LLMs can help by both proposing potential hypothetical questions, as well as by crafting them to be sufficiently accurate and concise. See § 1.1[C].

Example:

Q: Dr. Necessiter, I ask you for your opinion based on the following facts: Assume that on June 21, a thirty-nine year old man was employed as a groundskeeper in the Chicago school system. He was riding a lawnmower on the grounds at Quigley High School, which were hilly and wooded. This man was mowing at about a speed of three miles per hour. His hands were on the controls while he looked ahead and occasionally had to look to the sides and behind. The mower hit a stump that stuck out of the ground about eight inches high and twenty inches wide. The force of the impact knocked the man off the seat of the mower and he fell to the ground. He hit his head on the turf and became unconscious. A passerby saw the accident and came to his aid. When the man became conscious, after about five minutes, the passerby took him to Rush Hospital where he was examined. The examination included an MRI of his head. The test results revealed a four inch fracture line on his skull which extends from the anterior side of the external auditory meatus through the middle of the right parietal bone. The man complains of severe headaches.

Dr. Necessiter, assuming all these facts, do you have an opinion based on a reasonable degree of medical certainty whether the injury suffered by Groundskeeper Willie to his head was caused by the fall from the mower?

A: Yes I do.

Q: Please tell us that opinion.

There is a tendency to oversell a case with a hypothetical question and ask the expert to give an opinion beyond the expert’s capability. The hypothetical question should not be used to argue the case. The more that is included in the question, the more there is a chance for exaggeration and error, and the more opportunities there are for the cross-examiner to challenge the basis of the expert’s opinion.

E. Narrative Responses

Direct examination tactics for expert witnesses parallel many of the approaches and techniques applicable to a lay witness. There are some significant differences in questioning techniques. A direct examiner usually wants an expert to answer broad questions with detailed narrative responses. Judges, arbitrators, and ALJs typically allow expert witnesses significant leeway. Many experts testify as if they were a teacher or professor explaining information in understandable language.

Accordingly, experts are permitted to testify with narrative responses. The attorney needs to maintain an interesting and energetic dialogue and retain control over the direction of the testimony and ask specific follow-up questions that develop the conclusions of the expert. Some experts with legal experience can provide useful suggestions regarding how their opinion ought to be introduced and what questions should be asked. The advocate should monitor and interrupt answers if words or concepts need to be explained or if the expert is rambling or becomes incomprehensible.

F. Explaining Specialized Terms

The direct examiner must understand and know how to pronounce all of the expert’s specialized terms. Expert testimony often includes technical words and concepts because they establish a required foundation for an opinion or because they buttress the credibility of the expert. It is crucial to an understanding of the testimony that definitions of terms be fully explained. The expert should define technical terms after using them, or counsel should interrupt and ask the expert to explain the terms in plain, common, and understandable language.

Examples:

Q: How does a stethoscope work?

Q: What is a CAT scan?

Q: You used the term “metacarpals.” What are they?

Q: Chief Sitting Bull, how does a surveyor complete a triangulation?

Example:

Q: Did your business partner, Reginald Leigh Dugmore, fly a drone over the State Capitol?

A: Yes.

Q: How did that happen?

A: I was there. It was inadvertent. He was using FPV goggles.

Q: What does FPV mean?

A: First person viewing. His goggles provided him with the view.

Q: Can the drone be programmed to avoid this occurring again?

A: Oh, yes. We are able to prevent it from happening again.

Q: How is that?

A: We successfully re-designed the directional system.

Q: Explain the system that can be installed on a drone aircraft to keep this from happening in the future.

A: A firmware device can be installed on a drone with GPS to prevent it from flying over restricted areas such as the State Capitol.

Q: Explain what you mean by the term firmware.

A: Firmware is the combination of computer data and a program code which directs the control system.

Q: Explain the term GPS.

A: The Global Positioning System—GPS—is a space-based satellite navigation system that provides guidance to the firmware.

Q: Tell us in layperson’s language what that means and how it effectively works.

Technical terms need to be correctly spelled for an accurate record. Counsel should provide the court reporter with a list of terms the expert uses.

Demonstrative exhibits and visual aids may be used to help experts explain information. Charts, diagrams, models, digital presentations, and computer-generated graphics may be prepared which illustrate what an expert describes. For examples: A drawing of a gas chromatograph (a device that measures blood alcohol levels) will help explain the testing process. A model of a human figure allows a doctor to explain relevant body parts. A video recording which shows a testing procedure demonstrates visually what is difficult to describe orally. An illustrative slide may list definitions. A visual aid may be created by counsel while the expert testifies by writing key words on an easel pad, smart board, or computer screen. Gen AI can help produce instructive illustrative aids. See § 8.3.

G. Treatises

Treatises include books, periodicals, articles, website compositions, specialized internet sites, and reliable LLM-backed platforms (grounded in trustworthy sources). Treatise statements and content may be used on direct or cross-examination. The authenticity of a treatise may be established by a reliable authority, through the admission of a witness, through another verifying expert or through judicial, arbitral, or administrative notice. Portions of a treatise may be introduced as evidence for any purpose. Treatises need not become exhibits, and contents of a treatise offered in evidence are part of the record.

When a treatise is in general use and is relied on in a particular field, most experts will admit that it is an authority. An expert cannot prevent being cross-examined with a well-recognized treatise by suggesting the treatise is unreliable. If any expert is able to testify that the treatise is authoritative, it may be used to cross-examine another expert, even though that expert refuses to recognize the authority of the treatise. The authoritative portions of the treatise may be read by the lawyer or by the expert. This evidence may be offered for any purpose. Whether used for impeachment purposes or as substantive proof of its contents, treatise statements and content may substitute for a live expert and may corroborate an expert’s opinion.

Example:

Examining Lawyer:

Q: Doctor, are you familiar with a website article in the National Journal of Medical Research, entitled “The Diagnosis of Migraine Headaches Suffered by Law Students,” by Dr. Langdell?

A: Yes, I am.

Q: Have you read that article?

A: Yes, I have.

Q: Have you used the information in that article in your work?

A: Yes, I have.

Q: Do you consider it authoritative?

A: It is a very reliable authority.

By the Attorney:

Your Honor, if I may, I would like to read one sentence in part three of that article entitled, “The Diagnosis of Migraine Headaches Suffered by Law Students.”

Judge:

You may do so.

Examining Lawyer:

“The severity of a migraine headache of an average law student bears a direct causative relationship to the excess number of numbing online law school classes virtually attended by the student.”

Expert Cross-Examination

A. Preparing Cross-Examination

Thorough preparation for cross-examination of an expert begins during discovery and case preparation. Information must be obtained regarding the expert’s identity, qualifications, background, opinions, bases for opinions, supporting facts, publications, websites, prior cases, and fees. To effectively cross-examine an expert, the attorney must become knowledgeable about the area of expertise involved in the case. The same efforts the advocate employs in preparing direct examination applies to cross preparation, including the use of LLM-backed resources. See § 10.4(A).

B. Cross-Examination Areas

The cross-examination approaches and techniques explained in Chapter 9 that apply to lay witnesses also apply to expert witnesses. This section explains additional tactics that may be used to cross-examine experts, including both supportive and discrediting cross.

Supportive Cross-Examination

• Obtain helpful evidence.
• Secure useful concessions.
• Agree with favorable opinions derived from a reliable LLM.

Discrediting Cross-Examination

• Disclose expert fees and financial interests.
• Reveal bias or prejudice based on experiences.
• Expose unreliability of the purported area of expertise.
• Dispute the facts relied on by the expert.
• Challenge sources of information buttressing the opinions.
• Establish unreliability or insufficiency of bases of opinions.
• Emphasize the expert’s lack of knowledge about the case.
• Illustrate insufficient examination or testing.
• Verify existence of other causes.
• Uncover inappropriate or insufficient expertise.
• Confirm differences of opinions among experts.
• Contrast data and conclusions from reliable AI sources.
• Contest subjective opinions.
• Rely on admitted exhibits to contradict expert statements.
• Introduce inconsistent prior statements and positions.
• Discredit hypothetical questions.
• Use treatises to impeach.
• Highlight other deficiencies.

The advocate needs to review these techniques and determine which of them are applicable. Experts do not often change their opinion or admit making a major mistake on cross-examination. Openly attacking an expert opinion may not be productive. Direct and indirect challenges can reduce the reliability of the opinions and the credibility of the expert.

The attorney must control the responses of an opposing expert and not allow the witness to reply with damaging answers. Experienced expert witnesses who have testified in previous cases may be able to evade answering broad questions or attempt to defend their answers. Counsel may have difficulty controlling the responses from these experts if the cross seeks to explore questionable areas. Narrow and targeted questions based on evidentiary facts and sound opinions need to be carefully composed and asked. The last part of this Chapter presents specific areas and topics that may be probed to reduce the risk of losing control of an opposing expert while discrediting the testimony. See § 10.7(B).

C. Developing a Plan

It is important to develop an effective cross-examination plan, implement it, and revise it as necessary during the case. Following a plan prevents ill-conceived attempts by counsel to ask poorly prepared questions. A well-designed plan incorporates alternative lines of cross-examination that may be asked depending on the expert’s responses. Again, an LLM can assist with the preparation of cross areas and questions. See § 1.10(E).

A case may require experts to perform an examination, investigate a site, conduct tests, or review research to support their opinion. For example, an expert in a products liability case may be asked if a certain test was conducted. If the expert says “No,” the cross-examiner can proceed to demonstrate what this test would have revealed. If the expert answers: “It wasn’t necessary,” the cross-examiner may establish inappropriate choices the expert made and pertinent information that was not obtained.

D. Generative AI and Cross-Examinations

Generative AI and LLMs can significantly enhance the preparation for expert cross-examination. These AI tools can sift through vast amounts of information about an expert, such as prior testimony, publications, and professional background. They can quickly identify patterns, inconsistencies, and potential biases that may not be immediately apparent. Moreover, LLMs can summarize and analyze complex scientific or technical content, making it easier for attorneys to grasp the nuances of the expert’s field.

LLMs can also help generate a comprehensive list of potential questions and lines of inquiry for the cross-examination. By analyzing the expert’s previous cases and publications, LLMs can suggest tailored questions aimed at exposing the expert’s testimonial weaknesses or biases. Additionally, these models can simulate the expert’s potential responses, allowing attorneys to anticipate and prepare for different scenarios.

For example, an attorney preparing to cross-examine a medical expert in a malpractice case can use an LLM to review the expert’s past depositions and trial testimonies. This AI system might identify instances where the expert’s opinions have varied on similar medical issues, providing a basis for questioning the expert’s consistency. LLMs can also help the attorney understand complex medical terms and procedures, offering simplified explanations and highlighting critical points of contention.

Supportive and Discrediting Cross

A. Supportive Cross-Examination

The advocate ought to be able to identify some areas of agreement the cross-examined expert has with the advocate’s experts and case. Advocates can, in effect, make an opposing expert their witness for some matters. It is likely that opposing witnesses will agree on supportive issues, such as:

• Factual matters, including some of the underlying facts.
• The sequence of events and the way things happened.
• Objective favorable data gleaned from trusted sources.
• Opinions generally recognized in the expert community.
• Reasonable differences of opinions that exist among experts.

1. Obtaining Helpful Evidence

The opposing expert may be used to criticize a part of the opposing party’s position, statements or conduct. Questions can establish that what the opposing party said or did was inappropriate or otherwise deficient.

Example (Cross-Examination by Plaintiff):

Q: After the machine’s butterfly valve failed to close, the defendant did not replace the valve, Ms. Papillion?

A: That is my understanding.

Q: Had the defendant replaced the butterfly valve, Exhibit No. 2, at that time, this accident may not have happened?

A: It may not have happened.

Q: After the accident, the defendant removed the butterfly valve from the machine and left it outside?

A: Yes.

Q: Exhibit No. 2 was exposed to the sun, wind, rain and other elements of the weather?

A: Yes.

Q: The elements affected the condition of the valve as it sat outside for 59 days?

A: To some degree, yes.

Q: To a significant degree?

A: To a considerable degree.

Q: If the defendant had placed the butterfly valve in a safe protected environment, say inside a building, the condition of the valve would have been protected?

A: Oh, yes.

Q: You conducted tests on the valve only after it had been left outside for almost two months?

A: Yes, I did.

2. Securing Useful Concessions

An opposing expert may be used to establish, agree with, or corroborate positions and opinions propounded by supporting experts. Questions can be asked that obtain admissions regarding generally accepted theories, principles, and opinions among experts and which show that the opposing expert may well agree with the cross-examiner’s expert.

Example (Cross-Examination by Defendant):

Q: Mr. Hyde, do you agree with Dr. Jekyll that schizophrenia can be effectively treated with certain drugs?

A: Yes.

Q: One of those drugs is Schizophryn?

A: Yes.

Q: Another one of those drugs is Psychophryn?

A: In many situations.

Q: You heard Dr. Jekyll state that the conduct of the defendant on the day of the crime was a classic reaction of a person with a schizophrenic personality?

A: Yes, I recall that statement.

Q: You do agree with that conclusion?

A: In this case, I do.

This concession can be effectively used during summation: “The prosecution’s expert, Mr. Hyde, agreed with our defense expert, Dr. Jekyll, who testified for the defense in support of our position. He said. . . .”

B. Discrediting Cross-Examination

The most effective way to reduce the impact that an opposing expert has in a case is by discrediting the expert testimony. There are a variety of sources that can provide the bases for discrediting cross.

1. Expert Fees and Financial Interests

An expert usually receives money for time spent in preparing for and testifying at the trial or hearing. The amount of money paid may be introduced or emphasized on cross-examination. It may be reasonably inferred that the testimony of the witness is being influenced by the fee. Sometimes the fee is or appears to be excessive. Financial interests in a case can also be demonstrated if the expert has testified in similar cases for the opposing attorney or expects to testify in similar cases in the future. These fees and ongoing relationships infer that the witness has been influenced to testify favorably.

Example:

Q: Dr. Scrivello, you received a fee from the plaintiff’s lawyer for the hours you spent in preparing for this case, correct?

A: Yes.

Q: And you received a fee for the hours you are spending in court during this case?

A: Yes.

Q: You will be sending your bill for these fees to the lawyer for the plaintiff?

A: Yes.

Q: The amount of those fees that you receive will be more than $33,000?

A: Yes.

Q: You have been asked to testify in previous cases by the plaintiff’s lawyer, correct?

A: Yes.

Q: And you testified in several similar previous cases?

A: Yes.

Q: And you expect to testify again in the future?

A: I may.

The direct examiner will often bring out the existence of the fee, the amount of the fee, and involvement in previous cases during direct examination to reduce the impact of this area on cross. The direct examiner may also ask redirect questions allowing the witness to explain that the opinion has not been influenced by fees or financial interest. These areas may not be an effective topic for cross-examination if the cross-examiner expects to call an expert to testify on direct examination and that expert has similar fees and financial interests.

These questions need to be carefully crafted to avoid explanatory responses. The cross-examiner should not ask the question, “You are being paid quite a lot for your testimony today, aren’t you?” An experienced expert witness will reply that the payment is not for the testimony but is compensation for time, and that the charges are the same reasonable fees for time spent by the expert working elsewhere or testifying for others.

2. Bias or Prejudice

A professional expert witness who testifies frequently may have developed an apparent bias or prejudice because of involvements in previous cases. There are a number of experts who may only testify for one side because of circumstances (e.g., treating physicians who testify for injured plaintiffs), and there are experts who testify because of choice (e.g., insurance defense experts). Other witnesses may not testify exclusively for one type of party, but still may testify more often for either plaintiffs or defendants or prosecutors or criminal defendants.

The extent of the bias or prejudice is influenced by whether the expert has somehow been involved with the facts before liability arose or whether the witness was hired as an advisor to support the case. If a witness was a treating expert or was retained before the trial or hearing, the expert can be shown to have been a major participant in the case. If a witness was retained later in the action, the expert may have been influenced by knowing what opinion the lawyer wanted the expert to provide.

Example:

Q: Doctor Mendoza, you have testified approximately 20 times in court before?

A: Yes.

Q: Of those 20 times, 18 have been on behalf of the defense?

A: I believe so.

Q: Approximately 90% of the times you have previously been in court have been in support of the defense regarding the recovery of suppressed metadata from a computer?

A: Yes.

Example:

Q: Dr. Childs, all the information you used to form your opinion was sent to you by the plaintiff’s attorney?

A: Yes.

Q: The attorney told you that she represented the plaintiff?

A: Yes.

Q: The plaintiff’s attorney also told you she believed plaintiff’s injury was caused by the faulty Julia Childs cooking oven?

A: She did tell me that.

The direct examiner may anticipate this line of questioning and portray the witness as an independent professional who has high ethical standards. The direct examiner may also conduct redirect examination to reinforce the integrity of the expert.

3. Inadequate Sources of Information

Questions may reveal that an expert relied upon incomplete or inadequate sources of information in forming an opinion. The adverse inference is that the witness did not have all the available information necessary to form a proper opinion, or did not know of a source of information essential to forming an objective opinion. The witness may have received information primarily from the lawyer who hired the expert; the witness may not have had information accessible to other experts; or the witness may not have reviewed information vital to forming an opinion.

Example:

Q: Doctor Hellion, you based your opinion in this case on information that the defense attorney provided you, correct?

A: Yes.

Q: You were not present at the scene of the fire?

A: No.

Q: You never went to the scene of the fire, did you?

A: No.

Q: You never conducted your own investigation of the remains of the building?

A: I did not.

Q: You don’t have personal knowledge about how the fire started?

A: I do not.

Q: You relied exclusively on the information the defendant who hired you provided you?

A: Yes.

Q: That information was contained in documents given to you by the defendant’s lawyer?

A: Yes.

Q: You never talked to the owner of the building, who is the plaintiff in this case, did you?

A: No.

Q: You never talked to the fire marshal in this case?

A: No.

Q: You never talked to anyone except the defendant and members of the law firm representing the defendant, did you?

A: Correct.

Q: You never asked for any other information?

A: I didn’t have to.

Q: You didn’t think it was necessary to ask for additional

information?

A: I decided not to in this case.

Q. Did you ask for the additional information that was available to our expert, Dr. Dobsonfly?

A. I did not.

Q: You chose not to seek further data?

A: That’s correct.

Q: You relied on only what the defense provided you?

A: Yes.

4. Unreliable or Insufficient Information

Some experts may base an opinion on subjective facts obtained from a party. This is particularly true of treating or examining physicians, psychiatrists, or psychologists who obtain their information from a patient. The expert’s reliance on this information suggests their opinion is unreliable because of the partisan source of questionable facts.

Example:

Q: Doctor, you examined the lower back of Marion Barbara Carstair?

A: Yes.

Q: She told you she had some pain in her lower back, right?

A: Yes.

Q: She told you she thought the injury she suffered in the boat accident caused that pain?

A: Yes.

Q: You relied on her regarding her claim of lower back pain?

A: Yes.

Q: You examined her lower back carefully?

A: Yes.

Q: There was no bruising in the area of her lower back?

A: No.

Q: There was no apparent muscle spasm present, was there?

A: No.

Q: You relied on her, and her alone, for your initial opinion?

A: I had the information I wanted.

Q: You thought at the time you had enough information?

A: Yes.

Q: You performed no tests on her back?

A: It wasn’t necessary.

Q: Did you rely on any Medical Diagnosis tools?

A: I did.

Q: Which one?

A: The Salem MD.

Q: You only relied on that source?

A: That seemed sufficient.

Q: Another medical source may have provided other information?

A: Yes, maybe.

Q: You choose not to conduct any further searches, correct?

A: I didn’t need to do anything further.

Q: Well, you could have?

A: Perhaps.

Q: Perhaps, had you obtained additional information, you would have changed your opinion?

A: I can’t really say.

Q: In past cases, you have changed your opinion when you learned of

additional relevant information?

A: I have.

5. Disputed Facts

During direct examination the expert reveals facts that form the basis for the expert opinion. Some of these facts will be in dispute. On cross-examination the attorney can ask the witness if the opinion would change if the expert relied on other facts. If the witness agrees with this conclusion, the attorney can argue in summation that the opposing expert agrees with this favorable conclusion. If the witness disagrees, the attorney can argue that the opinion of the expert is suspect because the expert stays with the same opinion regardless of factual differences.

Example:

Q: Doctor Lavoisier, you based your opinion on the fact that the glucose content was five percent, correct?

A: Yes.

Q: If the glucose substance were only four percent, would that fact affect your opinion?

A: It might.

Q: And if the glucose was less than three percent that would change your opinion?

A: Yes.

6. Lack of Thoroughness

Experts have limited amounts of time to spend preparing and forming opinions. They may not prepare carefully or thoroughly. Questions can be asked to establish how little an expert has done and how much more an expert could have done.

Example:

Q: Marie Laveau, you are not a medical doctor, are you?

A: No.

Q: It’s fair to say you are a practitioner of scientific voodoo folkways?

A: Indeed, I am.

Q: You conducted a psychological examination of the defendant?

A: Oh, yes.

Q: You met with the defendant for an hour and a half?

A: Yes, I spent that time with her.

Q: Those ninety minutes were the only time you spent with her?

A: Yes.

Q: If you had spent more time with the defendant you may have acquired more information?

A: Sure.

Q: That additional information may have affected the opinion that you formed about the defendant?

A: It’s possible.

Q: You may have learned some things about the defendant you didn’t learn during your only interview with the defendant?

A: True.

Q: You don’t know what else you may have learned, do you?

A: I guess I don’t know.

Q: Well, we are not here to speculate, Ms. Laveau. It’s fair to say you don’t know what else you may have learned, correct?

A: Yes.

Q: And so, you don’t know how your opinion may have changed?

A: I do not know.

7. Insufficient Testing

An expert may not have conducted sufficient tests or procedures to support an opinion. The cross-examiner’s own expert can tell the examiner what tests an expert should have or could have conducted before being able to provide an opinion. Questions on cross can establish that the witness failed to conduct ordinarily necessary tests, did not obtain information experts typically rely on before forming an opinion, and may not have obtained crucial test results that may have changed the expert’s opinion.

Example:

Q: Dr. Crusher, you removed the cast two weeks after the break?

A: Yes.

Q: At that time, you didn’t test to determine any loss of weakness in the muscle?

A: Correct.

Q: You didn’t believe it worthwhile?

A: It wasn’t.

Q: You chose not to conduct a test because you believed you didn’t need to?

A: That’s right.

Q: You could have performed other tests rather easily?

A: I could have.

Q: And you didn’t conduct any test to determine any weakness in the nerve, did you?

A: I did not.

Q: You didn’t think that was necessary either?

A: I didn’t think it was.

Q: And you decided not to do any type of further tests?

A: That’s correct.

Q: You placed a new cast on?

A: Yes.

Q: You removed that cast four weeks later?

A: Yes.

Q: Some fractures require much more time in a cast, correct?

A: Yes.

Q: Serious fractures?

A: Usually.

Q: When you removed this final cast, you didn’t perform an electromyography, did you?

A: No.

Q: Isn’t it true an electromyography, if performed, would make it possible to demonstrate a weakness in a muscle or nerve before a permanent loss of strength developed?

A: In some cases.

Q: And this is a case in which that would be true, correct?

A: Yes.

8. Existence of Other Causes

Often there are alternative explanations for expert opinions. Cross-examination can reveal those alternatives by establishing other causes in addition to the cause the witness advances. The cross-examiner’s expert can provide these other possible causes of an event.

Example:

Q: Doctor Zhivago, there can be other causes for back pain, yes?

A: Yes.

Q: A degenerative condition can cause back pain?

A: Yes.

Q: Or stress?

A: Do you mean physical stress or mental stress?

Q: Physical stress?

A: Yes.

Q: And mental stress?

A: I suppose, yes.

Q: And infectious conditions?

A: Yes.

Q: Heredity?

A: Yes.

Q: Congenital conditions?

A: Yes.

Q: Even a preexisting injury?

A: Yes.

9. Inappropriate or Insufficient Expertise

The expertise of an expert may be in areas different from those directly involved in the case. A witness may have experience in a broad area, and the case may involve a very narrow area. Or a witness may have expertise on a very narrow subject, and the case may involve a broader subject. An expert may be vulnerable to challenges based on the lack of education, training or experience with a crucial issue in the case.

The emphasis attached to this area of cross-examination depends on how the opposing expert contrasts with the cross-examiner’s own expert. If a broad area of expertise is applicable to the case, the cross-examiner should attempt to narrow the expertise of the opponent’s expert. If a narrow area of expertise is appropriate in the case, counsel should attempt to broaden the expertise of the opponent’s expert.

Example:

Q: Mr. Verrazzano, your Master’s degree is in structural engineering?

A: Yes.

Q: You did not major in electrical engineering, did you?

A: I didn’t major in it, but I had some courses in it.

Q: Your experience has primarily been in the field of structural engineering?

A: Primarily.

Q: More of your professional life has involved structural engineering as contrasted with electrical engineering?

A: Yes.

Q: You have published numerous professional articles?

A: Yes, many.

Q: Those articles have dealt with structural engineering?

A: Yes.

Q: You have written articles on narrow bridge construction?

A: Yes.

Q: And you have written articles that have appeared in structural engineering magazines and on related websites?

A: Yes.

Q: None of those articles deal with the electrical engineering issues in this case, do they?

A: They do not directly.

Q: You have not relied on any of those articles as a basis for your opinion in this case, have you?

A: I didn’t need to.

Q: And that’s because those articles didn’t deal with the issues at stake in this case?

A: They do not.

10. Differences of Opinion Among Experts

Opinions in some areas of expertise are subject to significant and legitimate differences among qualified experts. This is especially true in fields of expertise involving subjective or interpretive fields, such as psychiatry or economics. Questions can establish that different experts have legitimate differences of opinion, and the testifying witness has been wrong sometimes and right sometimes in the past.

Example:

Q: Doctor Yellen, it’s difficult to predict with accuracy the rate of inflation for future years?

A: Yes.

Q: Prominent economists differ among themselves regarding the future rate of inflation?

A: Yes.

Q: This area of predicting the rate of inflation is subject to significant differences of opinion among experts?

A: Yes.

Q: You have been an expert economist for over thirty years?

A: Yes.

Q: During that span of time, you have periodically predicted the rate of inflation?

A: Yes.

Q: Sometimes your predictions have been accurate?

A: Yes.

Q: And sometimes your predictions have not been accurate?

A: Occasionally.

Q: You have disagreed with the predictions of experts whom you consider to be renowned in the field of economics?

A: Yes.

Q: And these experts who are authorities in their field and whom you recognize as authorities have disagreed with your predictions regarding the rate of inflation in the past?

A: I suppose.

Q: And sometimes their predictions—and not yours—have been accurate?

A: Yes.

11. Subjective Opinions

An expert may admit that the opinion the expert reached is a matter of judgment and not based on some immutable principles. This technique is useful for areas of expertise that are subjective in nature rather than scientific or technical. For example, opinions based on interpretations and beliefs can be effectively challenged.

Example:

Q: The assessment of the value of real property is not a science, is it Ms. Monopoly?

A: It may not be a science .

Q: There is no mathematical formula that yields a real property value

with certainty?

A: There is not.

Q: There are many variables that affect the value of a piece of property, correct?

A: Yes.

Q: Some of these variables are based on subjective evaluations and not objective data?

A: That is true.

Q. It is often a matter of individual judgement?

A. Sometimes.

Q: Some of these factors require an appraiser to interpret property values, correct?

A: Yes.

Q: And appraisers may reach different conclusions about the value of the same piece of real estate?

A: Yes, they may.

12. Inconsistent Prior Statements

An expert witness can be cross-examined using any oral or written statement made by that expert that contradicts or is inconsistent with a position taken on direct examination, as with a lay witness. A source that contains an expert’s previous statements can be used to locate impeachment. See § 9.7(A). An LLM can be instrumental in locating and providing prior statements. See § 1.10[E].

Example:

Q: Dr. Keynes, you testified on direct examination that the defendant used the FIFO method in this transaction because it is the preferred method utilized by accountants, is that right?

A: Yes.

Q: Doctor, you prepared a report summarizing your opinions in this case, didn’t you?

A: Yes.

Q: The attorney for the plaintiff retained you and paid you for your time in preparing that report?

A: Yes.

Q: Before preparing the report you thoroughly reviewed all the facts, correct?

A: Yes.

Q: You consider yourself an expert regarding accounting procedures, don’t you?

A: Yes.

Q: The report that you prepared was accurate, wasn’t it?

A: Yes.

Q: Doctor, I would like to show you your printed report. You do recognize this report, Exhibit 45, as the one you prepared?

A: Yes.

Q: Your signature appears at the end of the report on page 5?

A: Yes.

Q: Please turn to page 3, second paragraph, 4th line.

A: Okay.

Q: You wrote what’s contained on that line in that paragraph in that report, didn’t you?

A: Yes.

Q: You wrote on line 4 that: “Neither the FIFO nor the LIFO method is preferred in a case such as this.”?

A: Yes, I did, evidently.

13. Hypothetical Questions

If a hypothetical question is used on direct examination, an effective way to cross-examine the expert is to ask the witness concise hypothetical questions that contain relevant facts different from the direct examination hypothetical. This approach is similar to the technique discussed in Section 10.5(D) and can be used with similar success.

14. Treatises

Treatises can be used during the cross-examination of an expert to impeach that expert as well as for other purposes. Federal Rule of Evidence 803(18) and similar state rules provide:

• Treatises may be used on cross-examination of an opposing expert, or on the direct examination of an expert.
• Treatises include books, periodicals, articles, professional magazines, websites, and AI verifiable sources.
• Treatises must be established as “reliable authority” by admission of a witness or by another expert or by notice.
• Treatises may be introduced as evidence for any purpose.
• Treatises are read on the record and do not become exhibits.

Some experts who have written extensively may have published a position contrary to their position taken at the trial or hearing. Other experts may be impeached with treatises authored by others. This impeachment process requires a thorough review of relevant publications and a detailed index of these sources for use during the case.

An expert on cross-examination need only admit that a treatise is a reliable authority generally recognized in an area. The witness does not have to have relied upon the treatise or professionally agree to its position. Leading questions that establish that the treatise has successive editions, is used extensively in professional schools, or appears in the offices or smart tablets of many experts, may establish this foundation.

If an expert on cross-examination denies the general reliability of the treatise, the treatise may still be used but will need to be established as authoritative by another expert, the book editor, a librarian, or a website publisher. Some jurisdictions may require the witness on cross-examination to concede that the treatise is authoritative and that the witness relies on it before it can be used for impeachment.

The attorney proffering the treatise may read it to the fact finder or introduce it as evidence and it becomes part of the record. The treatise is admitted for all purposes: for impeachment, as substantive proof of its contents, to substitute for the views of another expert, or to corroborate another expert’s opinion. The opinion of an author of a treatise or other learned publication can be introduced through this authoritative source even though the author does not testify. See § 10.5(G).

Example:

Examining Attorney:

Q: Dean Wyeth, are you familiar with a text entitled, The Economics of Advocacy Practice?

A: Yes.

Q: This book has been a reliable authority in the field of law and economics for many years, correct?

A: Yes.

Q: Do you consider this text to be authoritative?

A: It’s one authority.

Q: Dean, do you agree with the following statement that appears on page 150: “The median salary for advocates is in inverse proportion to their LSAT scores and their law school class rank at graduation.”?

A: I would hope not. But, yes I agree.

To the Arbitrator:

I now would like to read a short paragraph from page 007.

Arbitrator:

You may do so.

Examining Attorney:

“The major factor bolstering the success of advocates in practice is their abiding affection for their favorite law school advocacy text.”

I have no further questions.

15. Safely Exposing Deficiencies

Additional areas that can be established on cross are topics that do not depend upon circumstances relating to the specific area of expertise. These areas include “safe” questions that can be asked if questions suggested in the previous subsections are not appropriate or are too risky.

• The late entry of the expert into the case. The opposing attorney may not secure an expert until immediately before the case is heard.
• The very limited amount of time the expert spent reviewing the information and data.
• The information the expert relied upon has been provided primarily by the party who retained the expert.
• The facts relied on by the expert are not the facts upon which other testifying experts relied.
• Other experts, the testifying expert recognizes as renowned, may hold contrary views.

Example:

Examining Attorney:

Q: Dr. Merit-Ptah, you’ve been working on this case for months?

A: Yes.

Q: You carefully prepared for your direct examination testimony?

A: I did, thoroughly.

Q: You understand there are very difficult issues in this case involving block chains and bitcoins?

A: There are.

Q: You’ve considered your opinions about these complex issues?

A: I have.

Q: And you also prepared to respond to this cross-examination?

A: I did prepare.

Q: And the answers you have given are your very best opinions?

A: The best I can offer.

Q: And the description you gave, about the difference between block chains and the bitcoins in this case, is the best you can offer?

A: It is.

16. Lack of Reliability of the Field of Expertise

This subject may be available if the advocate does not call an expert to testify in opposition to the other side’s expert or if an opposing expert claims an expertise that is questionable. The judge, arbitrator, or ALJ may permit the expert to give an opinion, but the opposing lawyer can still challenge the so-called expert. The advocate may ask cross-examination questions establishing the unreliability of the field of expertise or the failure of experts in related areas to accept and recognize the area as a reliable field of expertise. The cross-examiner may also show the expert opinion is not reliable nor credible. LLMs can be an effective tool for poking holes and finding flaws in unreliable opinions and untrustworthy conclusions. See § 1.1[C].

Topics that may be successfully covered using these approaches include:

• The lack of sufficient education, training, or experience of the expert.
• Differences between related areas of expertise that have been generally unrecognized.
• The failure to conduct necessary or needed examinations.
• The unreliability of the procedures or tests used.
• The observation that the field of expertise is merely the application of common sense that fact finders may apply on their own.

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