Faced with the problems of insufficient evidence, of conflicting evidence, and of evidence relayed through the flawed perceptual, retentive, and narrative abilities of witnesses, a jury is forced to draw inferences in its attempt to ascertain the truth.
By applying the same cognitive tools they have developed and used over a lifetime, jurors engage in the inferential exercise that lawyers call fact-finding.
In certain decision-making contexts that are relevant to the trial of lawsuits, however, these normally reliable cognitive tools may cause jurors to commit inferential errors that distort rather than reveal the truth.
Although juries can make a variety of inferential errors, most of these mistakes in judgment involve the drawing of an unwarranted conclusion from the evidence, that is, in reality, it does not prove.
For example, evidence that the defendant in a criminal prosecution has a prior conviction may encourage jurors to presume the defendant’s guilt, because of their preconception that a person previously convicted of a crime must be inclined toward repeated criminal behavior.
That commonly held belief is at least a partial distortion of reality; not all former convicts engage in repeated criminal behavior.
Also, a jury may give more probative weight than objective analysis would allow to vivid photographic evidence depicting a shooting victim’s wounds, or may underestimate the weight of defense testimony that is not delivered in a sufficiently forceful or persuasive manner.
Finally, complex or voluminous evidence might be so confusing to a jury that its members would draw totally unwarranted conclusions or even ignore the evidence entirely.
Recent empirical research in cognitive psychology suggests that people tend to commit inferential errors like these under certain predictable circumstances.
By examining the available information, the situation, and the type of decision being made, cognitive psychologists can describe the kinds of inferential errors a person or a group is likely to make.
These patterns of human decision-making may provide the courts with a guide to evaluating the effect of evidence on the reliability of the jury’s inferential processes in certain situations.
The fact that juries can commit inferential errors that jeopardize the accuracy of the fact-finding process is not unknown to the courts.
In fact, one of a presiding judge’s duties is to minimize jury inferential error through explanation and clarification.
Nonetheless, most judges now employ only a limited and primitive concept of jury inferential error: limited because it fails to recognize the potential for errors outside certain traditional situations, primitive because it ignores the research and conclusions of psychologists in favor of notions about human cognition held by lawyers.