The vast majority of convicted criminals are not incarcerated. Barely one criminal goes to prison for every 100 violent victimizations. And most violent prisoners serve less than half their sentence behind bars before being released. Surveys of prisoners show that most of them are violent or repeat criminals. More than 90 percent of state prisoners have committed one or more violent crimes or served a previous sentence to incarceration or probation.
Prisons do cut crime.
Millions of violent and property crimes are averted each year by keeping criminals off the streets. Prisoners released early are responsible for tens of thousands of crimes annually. Tripling the prison population from 1975 to 1989 may have reduced violent crime by 10 to 15 percent below what it would have been, preventing a conservatively estimated 390,000 violent crimes in 1989 alone.