Texas led the nation with a 144 percent increase in prisoners from 1991 to 1998 and had a decrease in crime of 35 percent, the study said. But two other populous states, California and New York, which had much smaller increases in incarceration California of 52 percent and New York of 24 percent had even sharper drops in crime. In another recent study, of the impact of the growth in incarceration on the drop in crime, Anne Piehl, an associate professor of public policy at the John F. Kennedy School of Government at Harvard University, drawing on changes in crime and prison data for each state, found that the increase in incarceration from 1989 to 1999 accounted for only about 5 percent of the drop in overall violent and property crime. Carlisle Moody, a professor of economics at the College of William and Mary who has long studied the link between incarceration and crime, criticized the new estimates of the effect of imprisonment, saying they were far too low because they did not take into account the recent history of prisons. The rate of incarceration has only recently begun to catch up with the crime rate.
Prison has a much greater effect on crime than anything else, like employment or policing.
The new book contains two studies of the impact of the growth in incarceration on the crime drop in the 1990's. Besides the study by Professor Rosenfeld, who estimated that incarceration reduced homicides by adults by 26 percent, a study by William Spelman, a professor of public policy at the Lyndon B. Johnson School of Public Affairs at the University of Texas, calculated that it reduced violent crime by 25 percent.