What Recent Studies Do (and Don't) Tell Us about Imprisonment and Crime

Despite three decades of study and a nationwide quasi experiment of unprecedented scale, it is still uncertain how large an effect prisons have on the crime rate. Researchers have learned some things along the way. We no longer use cross-sectional data sets because they make it impossible to separate simultaneous effects; we no longer use national time-series data and ratio variables because they produce inflated estimates. Better methods have improved the validity and narrowed the scope of recent estimates. Most studies show that doubling current U. S. prison capacity would reduce Index Crime rates by 20-40 percent. Nevertheless, some problems persist: simultaneity (just as prison affects crime, so does crime affect prison, and it is difficult to isolate one effect from the other); specification error (especially left-out variables); and difficulties in comparing among states (since different states use their prisons very differently). Perhaps most important, the range of estimates itself falls in an awkward spot. At the low end, further prison construction is probably not cost-effective; at the high end, it very likely is cost-effective. Given our uncertainty, further research as to the cost-effectiveness of alternatives to prison may be a better use of scarce resources.