Capital Punishment: More Con from Econometrics

Mark Thoma and I are both opposed to capital punishment. Mark points to some new ”evidence” that capital punishment deters murder:

According to roughly a dozen recent studies, executions save lives. For each inmate put to death, the studies say, 3 to 18 murders are prevented.

To paraphrase John Edwards, we’ve seen this movie before.



Jeffrey Fagan of Columbia Law School offered some interesting testimony a couple of years ago:

Recent studies claiming that executions reduce murders have fueled the revival of deterrence as a rationale to expand the use of capital punishment. Such strong claims are not unusual in either the social or natural sciences, but like nearly all claims of strong causal effects from any social or legal intervention, the claims of a “new deterrence” fall apart under close scrutiny. These new studies are fraught with technical and conceptual errors: inappropriate methods of statistical analysis, failures to consider all the relevant factors that drive murder rates, missing data on key variables in key states, the tyranny of a few outlier states and years, and the absence of any direct test of deterrence. 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 … In 1975, Professor Isaac Ehrlich published an influential article saying that during the 1950s and 1960s, each execution averted eight murders. Although Ehrlich’s research was a highly technical article prepared for an audience of economists, its influence went well beyond the economics profession … Over the next two decades, economists and other social scientists attempted (mostly without success) to replicate Ehrlich's results using different data, alternative statistical methods, and other twists that tried to address glaring errors in Ehrlich’s techniques and data. The accumulated scientific evidence from these later studies also weighed heavily against the claim that executions deter murders.

Dr.Fagan calls this research junk science but where have I heard of Ehrlich's results. Could it be when Ed Leamer was presenting his Let’s Take the Con Out of Econometrics? Mark says:

This is easy for me. It doesn't matter whether the research on the issue is valid or not. I'm against the death penalty.

Dr. Fagan would likely add that this new research is likely no more valid that the rest of the junk science we have seen.