Dr. Jeffrey Fagan, a professor at Columbia University Law School and a leading national expert on deterrence, testifed that recent studies claiming to show a deterrent effect to capital punishment are fraught with technical and conceptual errors. Fagan noted that a string of recent studies purporting to show that the death penalty can prevent murders use inappropriate methods of statistical analysis, fail to consider all the relevant factors that drive murder rates, and do not consider important variables in key states. During his testimony before committees of the New York Assembly gathering information regarding the future of the state’s statute, Dr. Fagan stated:

These studies fail to reach the demanding standards of social science to make such strong claims, standards such as replication and basic comparisons with other scenarios. Some simple examples and contrasts, including a careful analysis of the experience in New York State compared to others, lead to a rejection of the idea that either death sentences or executions deter murder…. A close reading of the new deterrence studies shows quite clearly that they fail to touch this scientific bar, let alone cross it.

For a full discussion of the problems identified by Dr. Fagan, read the text of his testimony in PDF format. (“Deterrence and the Death Penalty: A Critical Review of New Evidence,” Dr. Jeffrey Fagan, January 21, 2005). See also, Deterrence.