The prosecution are only going to bring a case if they think they can get a conviction, i.e. prove it beyond the jury's reasonable doubt. In effect, the prosecution are another jury, but one subject to several biases compared with the real jury:
So in general we should expect jurors to have a lower estimate of the prosecution's case than the prosecution themselves do.
In addition, cases only go to trial that are contestible -- where the prosecution thinks it can be proved beyond reasonable doubt but the defence does not. When the case is overwhelming and the accused is actually guilty, the accused is more likely to plead guilty without a trial. Jurors will never see those cases, only those that the accused finds worth contesting.
So it is not surprising that in a substantial proportion of cases, nobody can be sure of the jury's verdict until it is announced.
In addition, cases only go to trial that are contestible -- where the prosecution thinks it can be proved beyond reasonable doubt but the defence does not.
Or in cases where the defendant is, you know, actually innocent. Some people find that they can't stomach the idea of pleading guilty to a crime they didn't commit, whether or not they can prevail in court.
A new article looking at the jury system rationally and scientifically.
Excerpt:
This really struck me as something that could have been on LW's front page.