"One primary reason for sentencing an offender to prison is deterrence—conveying the message that losing one’s freedom is not worth whatever one gains from committing a crime. If imprisonment were an effective deterrent to drug use and crime, then, all other things being equal, the extent to which a state sends drug offenders to prison should be correlated with certain drug-related problems in that state. The theory of deterrence would suggest, for instance, that states with higher rates of drug imprisonment would experience lower rates of drug use among their residents.

"To test this, Pew compared state drug imprisonment rates with three important measures of drug problems — self-reported drug use (excluding marijuana), drug arrest, and overdose death — and found no statistically significant relationship between drug imprisonment and these indicators. In other words, higher rates of drug imprisonment did not translate into lower rates of drug use, arrests, or overdose deaths.

"State pairings offer illustrative examples. For instance, Tennessee imprisons drug offenders at more than three times the rate of New Jersey, but the states’ rates of self-reported drug use are virtually the same. (See Figure 3.) Conversely, Indiana and Iowa have nearly identical rates of drug imprisonment, but Indiana ranks 27th among states in self-reported drug use and 18th in overdose deaths compared with 44th and 47th, respectively, for Iowa.

"The results hold even when controlling for standard demographic variables, including the percentage of the population with bachelor’s degrees, the unemployment rate, the percentage of the population that is nonwhite, and median household income."