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Cross-Examining an Adverse Party's Expert Witness

By Howard S. Sussman, Esq.

By Howard S. Sussman, Esq.

Experts frequently appear as witnesses these days in all sorts of dispute resolution proceedings. That is true whether the proceeding involved is a domestic trial, a domestic arbitration or an international arbitration. The subjects about which expert witnesses testify of course differ to some extent among these types of proceedings, but the need to deal with expert witnesses, and to cross-examine an expert who testifies as a witness on behalf of an adverse party, remains prominent in all of them.

The principal function of an expert witness in any dispute resolution proceeding is to provide the decision maker in that proceeding with an opinion on some issue of significance to the resolution of the dispute that is involved. The credibility of that opinion, and of the expert who has provided it, are thus central to the cross-examination of any expert witness.

When you are confronted with an expert retained by an adverse party you must, therefore, find ways to minimize the negative impact of that expert’s testimony on your client’s case. The first step in finding those ways is for you to have your own expert. Your own expert will help you understand the field of expertise involved and how it bears on your client’s case, as well as providing you with essential information about the other party’s expert, including information about that person’s character and the position and reputation of that person in the relevant field of expertise. Your own expert will also help you to prepare your cross-examination of the adverse party’s expert. It is thus essential for you to have your own expert when the adverse party has retained an expert. It is also desirable for you to have your own expert, whether or not the adverse party has one, when you believe that your own client’s case would benefit from the insights an expert can provide.

How to Find an Expert

How you go about finding an appropriate expert depends, to a significant extent, on the nature of the case and your client. If the field of expertise is within your client’s business, you will often find that your client has an employee or a consultant who can lead you to an appropriate outside expert. But no matter how helpful your client’s own employee or consultant may be in educating you about the relevant field of expertise, in helping you prepare your cross-examination of an adverse party’s expert, and in helping you find someone whom you could use as an expert witness, your client’s own employee or consultant will rarely if ever be an appropriate expert witness because of the risk of a claim of bias. Even if your client’s employee or consultant can help you in finding an expert, it can also be exceedingly useful to consult an online expert directory that contains lists of experts organized by geographic location and field of expertise. Expert Pages is an exceptionally good computer-based service of that kind.

If the field of expertise is one as to which your client is unable to help -- medical expertise, say, when you represent a plaintiff in a medical malpractice case -- you will find such computer-based services of particular help. You may also find it useful to turn to those of your colleagues who have worked on similar cases, to any friends you may have in the relevant field of expertise, and to internet searches of people active in the relevant field.

After your expert has educated you, and after you have reviewed whatever material you have on the adverse party’s expert, which will usually include a written report prepared by that expert setting forth his or her opinion and the basis of that opinion, you will need to prepare to cross-examine that expert. As a generality, any cross-examination of an adverse party’s expert witness is directed towards that witness’s credibility, towards showing the decision maker that the expert’s opinion is not to be believed, in whole or in part, or (rarely) in leading the expert to change that opinion on the basis of a change in the facts so that, as changed, the expert’s opinion supports your client’s case instead of damaging it.

Lines of Attack on Cross-Examination: Credibility and More

Cross-examination of an adverse party’s expert is largely focused on credibility, both because the credibility of the expert’s opinion is central to the value of the expert’s testimony and because it is usually very hard to attack an expert on any basis other than credibility. In addition, you will almost never want to attack an expert directly in that expert’s field, since the expert will almost always know more than you do about that field and you will therefore almost always lose that contest. You will thus be very careful in how you structure your cross-examination so as to be sure to avoid that kind of contest. There are exceptions to these notions, but they are rare.

These are among the lines of attack that you can employ against an adverse party’s expert:

(a) Is the expert adequately qualified to give the opinion? Does the expert have the appropriate educational credentials and the appropriate experience? Is the expert up-to-date in the relevant field? Is the expert’s competence within the relevant sub-field of the general field of expertise, or is the expert’s competence too general to be meaningful?

(b) What is the factual basis for the expert’s opinion and is that factual basis adequate to support the opinion? Did the expert do any independent investigation of the facts? Are the facts on which the expert relied consistent with the evidence in the case? Would changing some fact change the expert’s opinion?

(c) Is the expert’s opinion intellectually coherent? What intellectual steps did the expert take in reaching that opinion? Can any of those steps be challenged on grounds of intellectual incoherence or other intellectual error?

(d) Is the expert’s opinion consistent with standard learning in the field? With standard texts in the field? With what the expert has written on the subject? Has the field changed since the expert last wrote on the subject?

(e) Is the expert actually working in the field of expertise or does the expert largely or entirely make a living testifying as an expert?

(f) How is the expert being compensated? Is that compensation reasonable? Compensation contingent on the outcome of the case is never reasonable or proper.

In addition to these lines of attack, which are specific to expert witnesses, any expert witness is also subject to the same kinds of attack on credibility as is any other witness. Is the expert a credible person? Is the expert biased or prejudiced? Has the expert made prior statements that are inconsistent with the present testimony? And so on.

Different Types of Proceedings Present Different Types of Challenges

The general principles discussed above apply regardless of the kind of dispute resolution proceeding in which you are involved, but there are important differences in how you apply them in different kinds of proceedings.

Domestic court trials

With a domestic court trial, the first thing to recognize is that the decision maker (the judge, or judge and jury), the lawyers, and probably the parties and the witnesses, will almost certainly all share a common mother tongue and a more or less common set of social and cultural assumptions. Of course there are differences in what you would do in a trial to a judge alone, as opposed to a trial to a judge and jury, but culturally you will presumably feel entirely at home. You will have the benefit of a familiar system, including familiar substantive law and familiar rules of evidence, and a socially and culturally familiar environment. That will be true even if an interpreter is used for one or more of the witnesses. Cross-examining a witness through an interpreter often presents great challenges, but having to do that kind of cross-examination does not make the proceeding foreign.

Domestic arbitrations

If, instead, you are appearing in a domestic arbitration proceeding, things will be somewhat different. You will still have the common language and the common social and cultural assumptions, but the details of the proceeding will almost certainly be less familiar. The substantive law may be largely the same, though you will have less control over it, but the procedural law, including the rules of evidence, may be quite unfamiliar. You may also not have the same level of pre-trial discovery. You may well not have the sanction of perjury to use in an attempt to control a witness. You may often find that the direct testimony of witnesses is presented through written witness statements instead of through oral direct testimony. There will be differences in the environment if you have three arbitrators instead of one. There may be many other differences, some of them very significant, from what you would encounter in a domestic court.

International Arbitrations

International arbitration proceedings present even greater differences, and it is vital that you be aware of them in planning how to proceed and in actually cross-examining. There will be three arbitrators and they will probably come from three different countries. They will almost certainly not have a common mother tongue, and their competence in the language of the proceeding may well be uneven, with some of them highly competent and others less so. There will almost certainly also be differences in their educational backgrounds and in their professional training and experience, and they will quite probably have differing cultural and social assumptions. There will also quite likely be counsel from more than one country, perhaps with yet a fourth mother tongue, or even more, and with varying competence in the language of the proceeding and differences in educational backgrounds and professional training and experience. You will have to take these multi-cultural factors into account in all that you do.

The proceedings will also be different from what you would find in a domestic court, and even from what you would anticipate in a domestic arbitration. There will have been a very extensive exchange of information in advance of the main hearing, but you will not have had any pre-trial discovery of the kind you would have in an Anglo-American court. You will rarely encounter oral direct testimony and witnesses, including expert witnesses, will almost always give their direct testimony by means of written witness statements. Your ability to surprise a witness will be much reduced from what you might find in a domestic court, or even a domestic arbitration, since adverse witnesses will have participated in the preparation of their written witness statements and will usually know of anything they may have said, written or done that would appear inconsistent with those statements. Counsel who called them will be equally well-informed. You will know, well in advance of the main hearing, what each witness will say, but you will not have much if any chance to see the witnesses live before you cross-examine them.

There will usually be no rules of evidence, which will mean that the arbitrators will receive into evidence whatever any party chooses to offer. But you may well have a lesser sense of the weight the arbitrators will give to any particular piece of evidence since the arbitrators will exercise their power and duty to evaluate evidence when they deliberate in private. There will generally be no subpoena power, no risk of perjury for knowing false testimony, and none of the other things to which you are accustomed in a domestic court.

There will also be far more time pressure to move things along than there would be in a domestic court. Partly as a result of that pressure, you will generally need to keep your cross-examinations shorter than they might be in a domestic court, or even in a domestic arbitration. You may even find that, as a result of the extensive exchange of information before the hearing, you have less of a need to cross-examine since the material you need may already be in the record. And the presence on the tribunal of arbitrators whose tradition does not include extensive cross-examination may lead you not to cross-examine at all even if you would have cross-examined if the matter were being tried in a domestic court.


Regardless of the nature of the dispute resolution proceeding, you will thus have a lot to think about when you consider whether, and if so how, to cross-examine an adverse party’s expert witness. You will need to evaluate that expert and that expert’s report for whatever vulnerabilities your own expert can help you uncover. You will need to decide whether those vulnerabilities are sufficient to attack the expert’s opinion, and what to do if they are not. And if you decide that you can and should cross-examine that expert, you will then need to consider the nature of the dispute resolution proceeding in which you are involved and whether the ammunition you have can be used effectively in that proceeding.

In doing these things, you should always remember the primary rule of survival as a cross-examiner: Don’t cross-examine unless you have both a very good reason to do so and also a realistic basis for believing that your chances of remedying the damage the witness did on direct examination are meaningfully greater than the risks of making that damage worse by an unwise or ineffective cross-examination.

Author’s Disclaimer: The foregoing is intended for general informational purposes only and is not intended, and is not to be used or relied upon, as legal advice of any kind. Neither Expert Pages nor the author will be liable for any damages or loss of any kind whatsoever -- direct, indirect, compensatory, punitive, consequential, proximate, economic, financial, or of any other kind -- that may result from use of or reliance upon the foregoing. Consult your own lawyer for legal advice.