The Illustrated Guide to Criminal Law Chapter 4: Deterrence Page 8: Negligible Effect
In sentencing a typical offender to, say, 5 years in prison, the general deterrence that results is basically ZERO. Because almost nobody will ever know about it.
The perception that drives GENERAL deterrence comes merely from one’s overall impression of how likely it is that, in this community, the guilty will be caught and then punished. This impression is more likely to come from TV, movies and urban legend than from any actual data.
Meanwhile, the SPECIFIC deterrence of giving John Doe those 5 years is also negligible. Those who ARE deterred are not affected by the length of the sentence, so much as the desire to avoid ANY sentence in the future.
Recidivists, meanwhile, choose to re-offend regardless of the sentence they received, often ratcheting up longer and longer sentences without any apparent effect.