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The Long and Short of Death Penalty Deterrence

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Recent studies of the deterrent effect of the death penalty (since 2000) have been done mostly by economists. Abstracts and citations are collected here. Although not conclusive, the weight of the evidence favors a deterrent effect, regardless of what you may hear from the anti-side spinmeisters. These studies tend to look at long-term effects.

Earlier, there were many studies done by criminologists. These studies examined short-term effects. They would ask if homicides went down after an execution and whether it mattered if the execution was well publicized. The results were mixed, but many of these studies found no deterrent effect. I have long been skeptical of this method, because I do not believe the recency effect is as important a component of deterrence as these researchers seem to believe. In a sense, I give criminals more credit for intelligence than they do. I begin with the hypothesis that an awareness that the state has the death penalty and actually enforces it will cause some people to refrain from killing. That is consistent with the general principle that incentives matter in human behavior; anyone who claims that the death penalty is an exception has the burden of proof. Awareness of the death penalty may be heightened by a recent, well-publicized execution, but it doesn't go away in a month. So a finding that the recency component of the deterrent effect, if any, is below the level a study could have detected doesn't tell us anything significant from a policy perspective. It tells us nothing about whether there is a total deterrent effect, the sum of short and long term effects, which is what we really want to know.

The September issue of Criminology, volume 47, number 4, has a new study on the short term effects.


The article is by Kenneth Land of Duke U., Raymond Teske of Sam Houston S.U., and Hui Zheng of Duke. The title is The Short Term Effects of Executions on Homicides: Deterrence, Displacement, or Both? Here is the abstract:

Does the death penalty save lives? In recent years, a new round of research has been using annual time-series panel data from the 50 U.S. states for 25 or so years from the 1970s to the late 1990s that claims to find many lives saved through reductions in subsequent homicide rates after executions. This research, in turn, has produced a round of critiques, which concludes that these findings are not robust enough to model even small changes in specifications that yield dramatically different results. A principal reason for this sensitivity of the findings is that few state-years exist (about 1 percent of all state-years) in which six or more executions have occurred. To provide a different perspective, we focus on Texas, a state that has used the death penalty with sufficient frequency to make possible relatively stable estimates of the homicide response to executions. In addition, we narrow the observation intervals for recording executions and homicides from the annual calendar year to monthly intervals. Based on time-series analyses and independent validation tests, our best-fitting model shows that, from January 1994 through December 2005, evidence exists of modest, short-term reductions in homicides in Texas in the first and fourth months that follow an execution--about 2.5 fewer homicides total. Another model suggests, however, that in addition to homicide reductions, some displacement of homicides may be possible from one month to another in the months after an execution, which reduces the total reduction in homicides after an execution to about .5 during a 12-month period. Implications for additional research and the need for future analysis and replication are discussed.
At the end of the Data and Methods section, the authors say this:

In sum, it should be emphasized that the objective of this model-building strategy is not to explain secular or long-term trends up or down in homicides or homicide rates in Texas--which is the focus of the recent round of analyses of annual time series of panel data for the 50 U.S. states cited--but the month-to-month fluctuations of these counts above or below the secular trends. In other words, net of the secular trends up or down in both time series, we seek to ascertain whether any evidence exists for the association of month-to-month fluctuations in executions with subsequent month-to month fluctuations in homicide counts in Texas, especially during the years 1994 to 2005 of high levels of executions.

If I understand this correctly, whatever short-term deterrence this study finds is in addition to whatever long-term effect may exist. The authors are skeptical of any long-term effect, but this study is not designed to test whether there is one.

So, from the short-term effect alone, they estimate that an execution saves between .5 or 2.5 lives, or, to get rid of the decimals, 10 executions in a year would save 5 to 25 lives.

That would be sufficient by itself to justify the death penalty, but short-term deterrence is not the only reason. There are long-term deterrence, retribution, and incapacitation as well.

This is just one study, but it is one more piece in the puzzle.

The article also includes one anecdotal nugget:

During a seminar presentation of the results from the present research by one of the authors, a colleague recalled the following incident. Some years ago his mother was in her late 70s and living alone in an apartment in Westchester County, New York. She had several collectibles. One afternoon the door rang, and two men, who must have known about her collectibles, forced their way in. They bound her to a chair while they went around the living room where most of her valuables were displayed. After they had taken what they wanted and were about to exit, one said to the other: "She has seen us and can identify us, should we kill her?" "No," answered the other, "we don't want to risk the death penalty." And so, to the great relief of my colleague's mother, they left her alone. This incident illustrates the kind of "second thought" process that may occur during instrumental crimes but is less likely to occur during highly emotional interactions.

If this happened again today, she would be murdered, thanks to the New York Court of Appeals.

Killings during "highly emotional interactions," by the way, are generally not capital murder. The typical case where people who know each other get into an argument and one flies off the handle is usually second-degree murder or voluntary manslaughter. Capital murder generally involves a premeditated killing or a killing in the course of another crime that is premeditated.

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From Joanna Shepherd's abstract on the CJLF website: (The link needs to be updated).

"In addition, capital punishment deters murders previously believed to be undeterrable: crimes of passion and murders by intimates."

Nit Pick: I know of no literature which states a belief that such murders were never deterrable.

By definition, only in cases of uncontrollable passion and rage, would such murders be undeterrable. Logically, in all other cases, the vast majority, neither passion nor rage are uncontrollable.

Furthermore, she finds:

"Moreover, murders of both black and white victims decrease after executions. This suggests that, even if the application of capital punishment is racist, the benefits of capital punishment are not. However, longer waits on death row before execution lessen the deterrence."

"Results from least squares and negative binomial estimations indicate that capital punishment does deter: each execution results in, on average, three fewer murders."

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