From the Cutting Room Floor: The Rationality of Juries
By Bryan Caplan
The earliest draft of “Rational Ignorance vs. Rational Irrationality,” (2001. Kyklos 54, pp. 3-26) was unpublishably long. Here’s one of my favorite “deleted scenes”:
rules of evidence [almost] explicitly assume that jurors are not rational. Judges weigh information’s “probative value”
against its “prejudicial effect,” and only allow a jury to see it if the former
outweighs the latter. But if jurors had
rational expectations, seeing graphic photos of the murder victim would not
provoke them to convict an innocent person.
Similarly, juries are rarely able to see evidence about a defendant’s
prior criminal record; the assumption being that juries would systematically
over-weight its significance.
A juror’s vote, unlike a citizen’s vote in an
election, often has a high probability of being decisive for the case at
hand. But it is the overall legal
climate – not the outcome of one case – that affects a juror’s wealth; and as a
rule the outcome of one case has no appreciable impact on the overall legal
climate. A juror’s private cost of
irrationality is therefore as trivial as the voter’s; the juror’s personal
wealth will not vary no matter how ill-founded his opinion is.
facing this incentive structure tend to consume a lot of irrational beliefs
about the probability that a defendant is guilty. Nothing deters them from believing that
handsome defendants are less likely to be guilty, or that DNA evidence is
unreliable. As a second-best solution,
the legal system hides some kinds of evidence from juries when they are likely
to respond irrationally to it.
Question: To what extent are the rules of evidence reasonable ways to compensate for juror bias? To what extent do they instead reflect the irrationality of legislators and judges?