Wow. Some very thoughtful and perceptive comments were posted yesterday on the basic question of why federal judges are more likely to acquit than federal juries. This is fun.

Let me pick up on a few of the points that people raised in their posts, to show what the data revealed. These figures are based on a study of about 77,000 federal criminal trials completed between 1989 and 2002. Those who read yesterday's post will recall that I am trying to figure out both why judges are more likely to acquit than juries, and why the judicial conviction rate dropped sharply between the late 1980s and the early 2000s.

Several folks hypothesized that the type of crime involved -- violent, property, drug, etc. -- might explain the disparity. Perhaps certain types of crimes are both steered toward a particular factfinder and are particularly likely to end with an acquittal. For example (I speculated), financial and regulatory crimes might be directed toward judges because both sides worry that jurors will misunderstand the evidence, and perhaps it is also the complexity of these cases that make them hard for the government to win. Or perhaps defense counsel avoid juries in violent crime cases, and so on.

There may be something to this, but the figures don't show much of an effect by case type. I looked at six crime categories: violent, property, drug, immigration, regulatory (crimes involving customs, social security, the mail, etc.) and public order offenses (a group that includes primarily traffic offenses -- really -- and guns). Two things became clear: (1) juries always convict more than judges, no matter what category of crime, usually by 15 to 30 percentage points, and (2) defense counsel prefer juries to judges in all types of cases. In only one category did the percentage of bench trials come close to half: 45% of public order trials are tried by the court. Interestingly, judges convict in only 47% of the public order cases, compared to an 83% conviction rate by juries.

Another line of posts offered the insight that the "conviction gap" might be explained by the strength of the evidence. To paraphrase Judge Posner, perhaps innocent defendants want judges because they worry about a mistake being made, while guilty defendants want a jury trial, hoping a mistake will be made. I think this explanation has great intuitive appeal.

But two brief points on this. First, it is darn hard to measure the strength of the evidence, at least on a large scale. The best indicator we have of the case strength is the outcome, but that leaves us chasing our tail if we are trying to evaluate the outcomes. This doesn't make this explanation wrong, it is just hard to know if it is right.

Second, if strength of the evidence explains a big piece of the conviction gap, we still need an explanation for why the jury conviction rate has remained steady while the bench rate fell significantly over the period studied. So while I like this explanation very much, I worry it is still speculative and incomplete.

I have left out a lot of detail, much of which I hope is provided in the article (on SSRN, at http://papers.ssrn.com/sol3/papers.cfm?abstract_id=843606 and perhaps in other posts later this week As always, questions and comments welcome at aleipold@law.uiuc.edu.