The Sunday New York Times Magazine has an article, Sentencing by the Numbers, discussing the junk science of predicting future criminality, and how some states, like Virginia, now are using crime statistics for the same purpose in deciding the length of sentences:

In 2002, the Commonwealth of Virginia began putting such data to use: the state encourages its judges to sentence nonviolent offenders the way insurance agents write policies, based on a short list of factors with a proven relationship to future risk. If a young, jobless man is convicted of shoplifting, the state is more likely to recommend prison time than when a middle-aged, employed woman commits the same crime.

....It's not a foregone conclusion that Virginia's method of sentencing is permissible under the Constitution, though no young male offender has brought a court challenge so far. Age and sex are what the law calls ''immutable characteristics,'' and it's a fundamental principle of antidiscrimination law that the government has to tread carefully when it treats people differently because of qualities that are beyond their control. (Being married or holding a job are different, but not entirely so, since these statuses reflect people's opportunities as well as their preferences.)

Grits for Breakfast has more criticism of the policy, warning it could violate equal protection guarantees.