The judge is out on juries

Is the traditional jury system in trouble? The first crown court criminal trial in England and Wales without a jury in 350 years is being held right now, dealing with the Heathrow robbery of 2004. The Guardian discusses the problem of keeping potentially prejudicial Internet information from modern juries. Are we seeing an erosion of having fair trials by one's peers, or the start of updating an old system to modern standards?

Juries are in the Anglo-Saxon legal tradition finders of fact: they are supposed to watch the legal proceedings, deliberate amongst themselves and produce a verdict. While there are many kinds of legal constraints on juries they also have moral constraints: bad jury behaviour can harm people and cause injustices to happen. The process should be competent (the jury should understand what is going on) and fair (not biased towards one side of the case or another).

The problem with competence is that the cognitive demands on the jury are quite strong. They have to listen to long presentations that are often technical, they are subject to both stress, boredom and social isolation, trials can last for a long time and yet they are supposed to recall all relevant facts during deliberation. Memory research rather unequivocally suggest that juries tend to be both forgetful and suffer from information overload. Worse, human memory has various biases that may affect jury decisions (e.g. something causing an emotional reaction is easier to recall than something neutral, there is little correlation between how well we think we can remember things and our actual accuracy) and these can be exploited.

During deliberation other biases come into play. It has been shown that during group deliberation information that is known by all members is far more powerful than information known to just a few. Forceful or unyielding members wield disproportionate influence (no matter whether they are right or wrong, neutral or biased). Deliberation often polarizes previously held positions rather than average them. People are easily swayed by the group, yet become overly confident in their judgement after deliberation.

This list of problem are only due to the properties of human thinking. There are obviously many other sources of bias (e.g. jury composition, external influences) and cognitive impairment (e.g. drug use, licit or illicit). The ideal picture of competence and fairness is hence rather far removed from the real courtroom situation. Some of these problems can be corrected by improving jury instruction, giving cognitive enhancers (whether notebooks or drugs) to jurors and structuring the proceedings in certain ways, but there is a limit to what can be achieved within the given structure.

In general it seems that reducing bias is more important than improving competence: a completely random jury will on average be right 50% of the time, but a biased jury is going to be unfair with a higher probability. An innocent found guilty by an incompetent jury has been subjected to an injustice but this injustice is general and not directed specifically at them, while an innocent found guilty by a biased jury has not just been subjected to the general injustice but also an injustice directly aimed at them.

Are we better off without a jury? In the Heathrow case the judge
decided on the jury-less case because there was a “very significant
danger” of jury tampering. If this is correct, then it may have reduced the bias. But it may only apply to very special cases. Without the danger of jury tampering the potential biases of a lone, small or large jury are hard to estimate: certain biases due to deliberation increase with size, while others due to individual biases decrease somewhat. There is no ideal size, as far as we know.

A proposal would be to take findings from decision making to heart and remove group deliberation. In many cases deliberation does not contribute to making better decisions but just increase bias, while averaging independent judgements does produce better decisions. Instead of deliberating the jurors (after some delay where they individually consider the case) just write down individual verdicts and a majority vote is taken.

The jury system originated with Germanic traditions of having men of good character investigate and/or judge crimes. It did not originate from considerations of the cognitive limitations and social complexity of holding trials in a modern society. While the goals of competence, fairness and social representativity remain unchanged, the means by which they might be reached can and should change with time. It is not inconceivable that new results in decisionmaking psychology, cognitive science or online collective intelligence may enable entirely new ways of achieving them.

For a popular overview of the limitations and possibilities of deliberation (and other decisionmaking methods) in the light of experimental psychology, see Cass Sunstein's book Infotopia.

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