Others want to know which deterrent is more effective - certainty of punishment or severity of punishment. General Evidence that Punishment Deters. Isaac Erhlich's 1973 study of punishment and deterrence is perhaps the most widely cited in the field. Another study, by Llad Phillips, found that each year of prison prevented 187 crimes per year. 21 Certainty of Punishment vs. Severity of Punishment.
Scholars regularly consider which provides the greater deterrent.
One provocative study involved prisoners and college students. When tested, both groups responded in virtually identical terms. Prisoners could identify their financial self-interest in an experimental setting as well as students could. However, in their decision making, prisoners are much more sensitive to changes in certainty than in severity of punishment. 23 Supporting evidence for this viewpoint comes from a National Academy of Sciences panel which estimated that a 50 percent increase in the probability of incarceration prevents about twice as much violent crime as a 50 percent increase in the average term of incarceration.