Just How Certain Should an Expert Witness Be?

Via Barking Up The Wrong Tree, are uncertain experts more persuasive than experts who are firm in their convictions?

Experts are more persuasive when they seem tentative about their conclusions… But the opposite is true of novices, who grow more persuasive with increasing certainty.

In one experiment, college students were randomly assigned one of four variations of a restaurant review, praising a local Italian spot. In some versions, the reviewer was described as a famous food critic; in others, he was a technology worker at a local college with a penchant for fast food. Each of the critics expressed positive certainty about the restaurant’s virtues in one variation, and tentative praise in another. Asked to evaluate the restaurant, the students who read the expert’s review liked it much better when he seemed tentative; the opposite was true of the novice.

I wonder how this might play out with the use of expert witnesses in trials. In an expert witness showdown, both sides often seem to be lobbing absolutely-certain experts at one another, each with contradictory but adamantly endorsed opinions. For any case that is technically or scientifically complicated, it’s an open question about how much of the substance of the presentation that the jury really comprehends. Since by definition the witnesses are experts on the subject they’re testifying to, jurors probably will not have the expertise to judge the merits of their testimony, so it comes down more to the witnesses’ demeanor and authoritativeness.

Obviously, trial strategy should be based on something a lot more thoroughly researched than a stray psych study. But I think it is at least plausible that in a battle of the experts situation, having a (well qualified) witness who gives a more reserved endorsement would be more persuasive than an opposing expert who is willing to follow his testimony to the grave.


1 thought on “Just How Certain Should an Expert Witness Be?

  1. I wonder how much experts actually are “absolutely certain.” In the interesting Supreme Court case of Delaware v. Fensterer, for instance, the expert couldn’t even remember the basis for his final conclusion. (The Supreme Court ruled that testimony was still admissible.) Makes me think that there might be more than a few test cases for your “less than certain” expert theory.

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