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The Relevance of Information Complexity to Jurors' Decision-making

Aug 17, 2007
There are three major factors that account for the difficulty the defense has with presenting a general causation case to a jury. They have to do with the ways in which people process information; the relevance of general causation evidence to what the jurors care about; and the complexity of the evidence. This article will discuss the third of these strategies.

That the expert testimony on general causation can be dense, complex, and uninteresting to jurors is not news. Yet there are ways in which it can be made less so. First, there is the use of language. Here too, getting the expert (or lawyer) to explain terms is not news. Yet we find that this effort too often occurs at too high a level; that there are terms that both the witness and lawyer take for granted that simply have different meanings to jurors. Susan Joy Hassel ("Talking to the Media" found on the UCAR Visiting Scientist Programs website) lists some of these terms.

They include: enhance, aerosol, ozone, exotic, positive and negative, radiation, model, sensitivity, manipulation, theory, reservoir, regime, proposal, sign, and significant. To take two examples from this list, for most people the term positive refers to something good while the term negative refers to its reverse which is very different from the meaning of an expert's testimony when he or she describes negative results..

It is best that substitutes for these terms be used. For instance, the witness can describe "a slight chance" rather than "a low probability." But more importantly the complexity of the expert's testimony can be decreased in some of the following ways:

1. At the start of the expert's testimony, summarize what the main points are rather than waiting until the end (do this before even going over the witness's resume, if possible). This same point applies within the testimony itself. An inductive discussion of a study where the bottom line is not given until the discussion is over is not a good way of presenting evidence. Most expert witnesses are led through a series of questions in which they will describe some study in detail and then conclude by giving the results of the study.

Sometimes these results are tied into the larger issue that is being addressed and many times they are not. It is far better that the initial questions focus on the results and why they are important to the case, followed by questions that delve into the study itself. There is nothing worse than a juror sitting in his or her seat saying, "Why is the witness telling me this?"

2. Try and inject some drama into the testimony. For instance, if an expert is discussing a study he did, have him talk about what excited him about the question he was asking; why, in human terms, the question was important; and the rush when he gained some new insight. Vivid narratives that engage the emotions and imagination of jurors are more effective.

3. In general, it is useful for the witness to raise the stakes of the science. After all, it is about why people live and die. A study poorly conceived or carried out can have dramatic effects on people by causing them to be improperly treated. The witness should communicate this.

4. Sometimes it is useful to use "peripheral" forms of persuasion when the topic is unavoidably complex. For instance, a witness who can state that, "There are seven reasons why the plaintiff's expert is wrong when he says x causes y," may be persuasive simply by saying that.

5. Most defense lawyers know what the plaintiff will say about the issue of general causation long before the trial begins. They know what their vulnerabilities are. There are effective ways to address these vulnerabilities. One of the most effective ways is to bring to the open what the jurors may be thinking.

For example, to ask a witness in a ground water contamination case, "Some people think that as long as a chemical gets on the ground it is going to get into the water under the ground. Is that so?" Or during closing in a chemical exposure case say something like, "When you are deliberating, you might hear another juror say, 'As long as those plaintiffs breathed a single molecule of the chemical, its likely the chemical injured them.' How might you respond to that? Well, first...."

6. Finally, we are all familiar with the use of analogies. Analogies are great when trying to explain a concept but less so when trying to make an argument. They are far too easily turned around and they require cognitive efforts on the part of jurors. Used to teach statistical concepts they can be very effective. To illustrate the hypothesis testing framework, an expert can use the analogy that in this trial the defendant is not liable until it has been proven that it is liable.

The difference between a type I and type II error can be taught by discussing the implications of finding the defendant liable when it is not and vice versa (in closing, when summarizing this expert's testimony, the jurors can be told that if they were to find the defendant liable they would be committing a type I error).

As another example, the idea that the average can be misleading because it ignores variability, the witness can describe the person with his head in a refrigerator and his feet in the oven who feels pretty comfortable because his average temperature is normal (for other examples, see Campbell, S.K. (1974), Flaws and Fallacies in Statistical Thinking, Prentice-Hall, New Jersey). Defense lawyers should also be on the lookout for great metaphors. Metaphors say what a thing is, not what it is like. They can be poetic and persuasive. The term "junk science" is a metaphor.


In everyday life, scientists and lawyers do not behave like scientists and lawyers. For jurors a trial is everyday life. They do not and will not reason like experts. To the lawyer and scientist, jurors may be making mistakes in their reasoning, but they are not. They are doing the reasoning of everyday life. How this is done with scientific evidence can be understood and consequently the evidence can be presented to them in a way that makes sense to everyone, lawyers, scientists, and jurors alike.
About the Author
David S. Davis, PhD is a founder of and principal in R&D Strategic Solutions, trial consultants and jury consultants specializing in jury selection, voir dire, and mock trials.
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