It’s been “reasonable doubt” week here at The Big Questions. We’ve talked about recognizing reasonable doubt when you see it, about what the standard should be, and about what the standard for determining the standard should be.

This raises the question: What is the standard? Here’s the weird part: Nobody knows. The judges won’t tell you and neither will the legislators. If you’re on a jury, you’re on your own.

Now you might say that that’s a fine thing. We want to leave it to jurors to set this standard. Under that theory, a juror has two separate questions to answer. One is “How doubtful am I?” and the other is “How much doubt counts as reasonable?”. But I don’t believe anyone actually subscribes to that theory.

Here’s why I say that: Suppose that in a murder trial, the foreman of the jury reports back to the judge that the jurors have agreed that there’s a 15% chance the defendant is guilty, and that they consider 15% to be beyond a reasonable doubt. Therefore they have unanimously voted to convict. I am not a lawyer, but I will cheerfully bet you that in any such case, the judge would throw the conviction out in a hurry, on the grounds that 15% is not at all beyond reasonable.

In other words, the judge does not subscribe to the theory that it’s entirely up to the jurors to set the reasonable doubt standard. Moreover, the judge would throw out the verdict at 16% or 17% or 18% and so on up to …. what? Well, up to some number. That number is a standard that the judge is prepared to enforce. What is that number? I bet the judge won’t tell you. The question is: Why not? Why doesn’t the judge say something like “You should convict if you are at least 90% certain the defendant is guilty”?

Continue reading ‘Blinded Justice’

Yesterday, I posed these questions:

Here I have a couple of urns. The one on the left contains 70 red balls and 30 black. The one on the right contains 30 red and 70 black.
While you weren’t looking, I reached into one of these urns and randomly drew out a dozen balls…4 of them were red and 8 were black.

1. If you had to guess, which urn would you guess I drew from?

2. What’s your estimate of the odds that you’re right?

3. Do you think you’re right beyond a reasonable doubt?

I stole this problem from the decision theorist Howard Raiffa, with some minor changes (he used bags instead of urns, and green and white balls instead of red and black — and he drew his twelve balls with replacement, rather than all at once, which has only a tiny effect on the probability). Here, with appropriate minor wording changes, is what Raiffa had to say:

Continue reading ‘Reasonable Doubts’