Confirmation Bias (Reisberg, Applied Cognition, ch. 13)

As Chapter 13 of the textbook describes, reasoning can be pulled off track by many factors, so that our conclusions are sometimes less logical, less justified, than we would wish. How does this apply to the courts?

In many trials, potential jurors are exposed to media coverage of the crime prior to the trial's start, and this pretrial publicity can have many effects. One concern is the pattern called belief bias. In the lab, this term refers to a tendency to consider an argument "more logical" if it leads to a conclusion that the person believed to begin with. In the courtroom, this could translate into a juror's evaluating the trial arguments not on their own terms, but in terms of whether the arguments led to the conclusion the juror would have endorsed (based on the media coverage) at the trial's start! This influence of information from outside the courthouse is clearly contrary to the rules of a trial, but jurors may be unable to resist this powerful effect.

As a related concern, consider the effect called confirmation bias. As the textbook chapter discusses, this bias takes many forms, including a tendency to accept evidence favoring your views at face value, but to subject evidence challenging your views to special scrutiny, seeking flaws or weaknesses in these unwelcome facts. This tendency can easily be documented in trials: In one study, participants were first exposed to a newspaper article that created a bias about a particular murder trial. Then the participants were presented with the trial evidence, and had to evaluate how persuasive each bit of evidence was. The results showed a clear effect of the newspaper article: Evidence consistent with the (biased) pretrial publicity was evaluated as being more compelling; evidence inconsistent with the publicity was seen as less compelling. This distortion, in turn, biased the participants' verdicts. As a result, the pretrial publicity didn't directly influence the verdict. Instead, the verdict was based on the participants' evaluation of the evidence. But this evaluation was influenced by the pretrial publicity!

In light of these results we might worry that the courts' protections against juror bias may not be adequate: In some trials, for example, jurors are merely asked, "Can you set aside any personal beliefs or knowledge you have obtained outside the court and decide this case solely on the evidence you hear from the witness stand?" Such questions seem a thin shield against juror prejudice. As one concern, jurors might not know whether they'll be able to set aside their prejudices or not. They might not realize, in other words, that they are vulnerable to belief bias, or confirmation bias, and so might overestimate their ability to overcome these effects.

Laboratory results tell us that belief bias and confirmation bias are powerful effects and often work in a fashion that is completely unconscious. This strongly suggests that the courts need to seek more powerful means of avoiding these influences in order to ensure each defendant a fair and unbiased trial. Possible solutions include stricter screening of jurors, or procedures that would make it easier to change a trial's location. In any case, it seems clear that stronger precautions are needed than those currently in place.

To learn more about this topic in cognitive psychology and the law:

See, in the textbook chapter, pages 438-441

Hope, L., Memon, A., & McGeorge, P. (2004). Understanding pretrial publicity: Predecisional distortion of evidence by mock jurors. Journal of Experimental Psychology: Applied, 10, 111-119.

Lieberman, J., & Arndt, J. (2000). Understanding the limits of limiting instructions: Social psychological explanations for the failures of instructions to disregard pretrial publicity and other inadmissible evidence. Psychology, Public Policy & Law, 6, 677-711.