tt.humanist :: forum :: commentary :: 2012 :: crime

Statistics for death penalty as a deterrent are dishonest

17 March 2012 • 276 words

In a letter published on 16 March 2012, one Shelton Stanford cited what purported to be seven studies showing that the death penalty had a deterrence effect on murders. On reading Mr Stanford’s seven citations, however, it turns out that he was repeating just four studies by the same people. One of those researchers, Goodwin Liu, is actually an opponent of capital punishment.

Richard Berk, Professor of Criminology and Statistics at the University of Pennsylvania, in an analysis of such studies, wrote: "A number of papers have recently appeared claiming to show that in the United States executions deter serious crime. There are many statistical problems with the data analyses reported. This article addresses the problem of 'influence,' which occurs when a very small and atypical fraction of the data dominate the statistical results. The number of executions by state and year is the key explanatory variable, and most states in most years execute no one. A very few states in particular years execute more than five individuals. Such values represent about 1 percent of the available observations. Reanalyses of the existing data are presented showing that claims of deterrence are a statistical artefact of this anomalous 1 percent."

If Mr Stanford was intellectually honest, he would change his mind about the death penalty in light of this. However, his inability to distinguish between 4 and 7 suggests that he does not understand even the simplest numbers. But Mr Stanford’s problem is not innumeracy but illiteracy, since he copied his letter virtually word for word from an article by Dudley Sharp, who describes himself as a “death penalty expert”, without crediting Mr Sharp <www.prodeathpenalty.com/deterrenteffect.htm>.

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