Also see the National Research Council (2014)'s report on the growth of incarceration in the US:

>Nevertheless, the evidence base demonstrates that lengthy prison sentences are ineffective as a crime control measure. Specifically, the incremental deterrent effect of increases in lengthy prison sentences is modest at best. Also, because recidivism rates decline markedly with age and prisoners necessarily age as they serve their prison sentence, lengthy prison sentences are an inefficient approach to preventing crime by incapacitation unless they are specifically targeted at very high-rate or extremely dangerous offenders. For these reasons, statutes mandating lengthy prison sentences cannot be justified on the basis of their effectiveness in preventing crime.