Yesterday’s Thoughts

September 27, 2005

Probability and the Justice System

For some time I’ve had a post in the queue on probability as tool for knowing. There were essentially two points, both of which pertained to sequence of facts required to reach a conclusion. 1) If your conjecture depends on a number of highly improbable events, it is unlikely to be true. 2) If your conjecture depends on a number of highly probable events, it is also unlikely to be true. I’ve explored this a little bit in Analyzing an Argument and Take the First Available Turn.

The take home message from this analysis is that the only way to certainty is to be certain at every step.

Certainty at any step is rare. Certain conclusions based on a sequence of statements must be extremely rare. The question is, how do we proceed.

I am interested in exploring the practical options.

It occurred to me today as I was rushing to pick up my children that the judicial system is one example of these axioms put into place for practical ends.

The goal of the judicial system is to determine the truth in a practical sense, or “beyond a reasonable doubt.” At the same time it is noted that poor and minority defendants are more likely to be arrested, more likely to be convicted, more likely to receive harsh terms and more likely to be sentenced to death for capitol offenses. (Yeah, I could use some references for that.)

One reason for the discrimination against poor and minority defendants should be obvious from a thought experiment.

Suppose you have two identical defendants, facing two identical police forces, prosecuting attorneys, judges, juries, appellate courts, etc. Discriminatory factor number one is that defendants with resources can keep the proceedings going longer. Since once you are acquitted the trial is over, the more chances you have at trial, the better your chances of ultimately getting acquitted.

The real analysis is somewhat more complicated because the appeals process normally kicks the trial back to trial court, but having a second shot doubles your chances for acquittal.

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