Factors Affecting Persuasiveness of Expert Witnesses - Part 1

Part 1 of 2

CSI - Courtroom Sciences Inc.

This article considers the significance of expert witness compensation and witness credibility from the standpoint of the defendant in a civil action; the conclusions are  equally applicable to plaintiffs' trial strategy and use of expert witnesses. While the discussion assumes the presence of an expert witness in a live jury trial, the principles discussed herein are equally applicable to videotaped depositions.

As a foundation, this article begins with a description of a three-dimensional theory of persuasiveness as it relates to expert witness credibility. This theory comprises the three witness credibility dimensions of expertise, objectivity, and communicativeness.  With those explanations as a backdrop, the effects of compensation and the frequency of testifying on the impact of expert witness testimony are then considered. The article concludes with a section of specific recommendations for enhancing the persuasiveness of expert witnesses.

Many familiar terms of witness credibility fit within the three-dimensional framework of expertise, objectivity, and communicativeness. For example, for a witness to be perceived as truly objective, as defined presently, he or she must also be judged to be "honest." ln addition, if he/she is seen as honest and having a high level of expertise, he/she must also be perceived as "trustworthy." Others may supply their own terms to fit this framework, or may indeed object to it, because one of their favorite intuitive labels has not been included here. However, this three-dimensional framework represents a   useful combination of parsimony and comprehensiveness in describing the performance of an expert witness.

A Three-Dimensional Theory of Persuasiveness 


It will be helpful to first define some basic  dimensions of witness expertise. ln common usage the term "expertise" generally  refers to a person's credentials, e.g., educational level, experience, and aptitude. Just as important to expertise, however, are a juror's perceptions of the witness's diligence, perceptiveness, accuracy, and consistency

Within the framework, an expert witness,  to have expertise, should be well-educated from a reputable university; have an impressive background of achievement outside of the university (experience); exhibit  flexibility, creativity, and intelligence (aptitude); demonstrate thoroughness and the ability  to apply himself or herself completely to the consummation of a given task (diligence); have a broad, unconstrained awareness of the parameters of a given problem (perceptiveness); use precision in measurement, assessment, analysis, and language (accuracy); and be able to utilize these qualities effectively across a variety of situations (consistency).


However, more than expertise is required of an expert witness to persuade a jury of his or her view of the case. Expert witnesses also have the burden of the requirement that they appear to be objective. In a rather extensive, longitudinal study assessing the dimensions of witness credibility, it was discovered that the most important quality an expert witness needed in order to convince a jury is objectivity. Most jurors expect a given witness to favor the side that retained the witness, but they must be convinced that the witness approached the investigation/assignment objectively. That is to say, the jury expects a credible expert witness to acknowledge that there can be more than one side to  an issue.

Obviously, the jury’s assessments of a dimension such objectivity are not conscious, or at least not labeled similarly, by most jurors. (Indeed, some jurors have difficulty determining which side a witness favors. It is not unusual for a juror to say that he or she is “surprised that plaintiff's witness X hurt the defense case.") These naïve and uninformed perceptions aside, in general, most jurors must be convinced of an expert witness's objectivity in order to be influenced by this testimony.

Objectivity in the present context is the  ability of the witness to consider equally  two or more alternative, conflicting interpretations of a given problem (e.g., the antecedent causes of an automobile accident).  Note that there is a fine distinction between perceptiveness (part of the expertise criterion) and objectivity: perceptiveness requires only awareness, whereas objectivity requires that two or more conflicting viewpoints are given genuine, thoughtful consideration. Furthermore, the demonstration of objectivity  requires that cross-examination questions be answered with an equal level of expertise  (aptitude, diligence, perceptiveness, accuracy, and consistency) as direct examination questions.

Perhaps. most importantly, demonstrating objectivity to a jury requires that the witness use expertise to empirically show to the jury why one of those conflicting views is in fact most probably correct. Objectivity also requires, for example, that the tests used for evidence be equally capable, on an a priori basis, of providing results that could support any of the conflicting theories of the case. In other words, objectivity requires that the tests are not “set up" in such a manner as to be capable of supporting only one side of the conflict.

Finally, the demonstration of objectivity requires that the witness be unencumbered by dislike, disdain, or any other subjective form of rejection of the plaintiff's case theory. His preference for the defendant's case must be completely a function of scientific evidence and rigorous application of his own preexisting expertise - in short, his desire to know the truth, whatever it turns out to be. Obviously, the expert witness who is perceived as objective will not normally be sim ply discounted as a "hired gun."  

A common plaintiff’s attack, which is  frequently used when the plaintiff's attorney does not understand the technical issues of the case, is that "the witness is a hired gun for the defendant. “The plaintiff's counsel points out that the witness has testified many times before for the defendant. The witness is frequently asked how much he has charged for this case and/or how much has made from the defendant in all of his past cases. The implication is that because the witness is a hired gun, he cannot be trusted to provide objective opinions.  Post-trial interviews reveal that plaintiffs' jurors frequently accept this bias argument. Strategies for overcoming this appeal to the jury are discussed following the consideration below of the third credibility dimension, communicativeness


The third burden of the expert witness is that he or she be communicative. This quality encompasses the ability to clarify arcane or esoteric issues so that they are comprehensible to one or more ordinary sophistication. A communicative witness is sensitive to the fact that what is simple to him may be hard for someone else to grasp – indeed, the learned language natural to an expert is usually more akin to a foreign language to the untrained juror. Moreover, the communicative expert witness must give the impression that he cares whether others understand. Such caring encompasses a factor of “pleasantness” and is reflected in: the choice of terminology he selects to explain or make analogies; his use of lucid visual aids; and the pauses he takes to give jurors time to assimilate information. It is also reflected in eye contact, speech rate, volume, articulation, vocal inflections, and even posture. Finally, the pleasantness of a witness is communicated by an aura of likeability and confidence. Such attributes are influenced by tone, attractiveness, attire, mannerisms, and facial expressions.  

Effective demonstrative materials will enhance the communicative aspect of credibility. Such demonstrative material may include models, computer simulations (animations), document blow-ups, photographic exhibits, graphic charts with overlays, and various other forms of visual aids. The point is that the use of dramatic demonstrative evidence makes the material more memorable, and it makes the witness seem more communicative and therefore, more credible. As communicativeness increases in this fashion, compensation, or the frequency of usage of the witness loses its salience in the minds and memories of jurors. 

Often, the issue of communicativeness comes through most strongly during cross-examination. By the time the defense case is presented, jurors have figured out that all expert witnesses can appear intelligent on direct examination. Only true experts, however, continue to appear confident, articulate, and non-defensive when being attacked by the attorney on the other side. 

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