Aggravated assault has decreased 14 percent, as the probability of prison has increased 27 percent. Burglary has decreased 18 percent, as the probability of prison has increased 14 percent. Moreover, once in prison criminals are staying there longer. Compared to the 1980s, the median prison sentence served by prisoners released in the 1990s has risen for every category of serious crime except aggravated assault. Roughly speaking, expected punishment is the number of days in prison a criminal can expect to serve per crime, as determined by the probabilities of being apprehended, prosecuted, convicted and going to prison, and the median sentence for each crime.
Evidence shows that potential criminals respond to incentives.
Crime increases when expected punishment declines, and vice versa. In response, the serious crime rate more than quadrupled during those years. In the 1980s, expected punishment began to increase, accompanied by the leveling off and then a decline in the serious crime rate. Between 1980 and 1996, expected punishment for serious crimes more than doubled, increasing from 10 to 22 prison days. Over the same period, the crime rate fell by one-third.