Live by the Study, Die by the Study

According to a NY Times story:

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. The effect is most pronounced, according to some studies, in Texas and other states that execute condemned inmates relatively often and relatively quickly.

I can only say one thing: ROFLe3!

That’s rolling on the floor laughing times 10 to the third power, i.e., 1000 times. Hell, make that ROLFe4! I’m really amused. After decades of leftists sneering down at the primitives in the red states who supported the death penalty, a virtual tsunami of studies demonstrates that capital punishment saves lives just like the hicks in the sticks thought.

It gets better:

A study by Joanna Shepherd, based on data from all states from 1997 to 1999, finds that each death sentence deters 4.5 murders and that an execution deters 3 additional murders.28 Her study also investigates the contested question whether executions deter crimes of passion and murders by intimates. Although intuition might suggest that such crimes cannot be deterred, her own finding is clear: all categories of murder are deterred by capital punishment.29 The deterrent effect of the death penalty is also found to be a function of the length of waits on death row, with a murder deterred for every 2.75 years of reduction in the period before execution.30 Importantly, this study finds that the deterrent effect of capital punishment protects African-American victims even more than whites. –[Sunstein PDF]

Capital punishment, the most evil of all the attributes of the racist American justice system, turns out to save the lives of African-Americans! I’m so tickled I can’t stand it!

There’s only one minor hitch in my glee: I don’t think these studies can possibly be measuring what they purport to measure.

All science begins with measurement. The precision and accuracy of measurements that create a scientific model’s data control its ultimate predictive power. Measurements in the soft sciences like economics and sociology notoriously lack accuracy and precision. We often have no clue if we are measuring the phenomenon we think we are measuring. For example, in the case of criminology, when measuring homicide rates, what events count as homicides? Each jurisdiction uses a different standard. The standards agree at the extremes but differ strongly in the grey areas in the middle. Ditto for sentencing. Almost any factor you care to measure — such as race, income, education, etc. — looks increasingly fuzzy the more one examines the details of the definition. (e.g., is Obama “black”, “African-American”, or “Other”?)

I personally believe that the death penalty protects the innocent and punishes the guilty. However, I don’t think we can accurately measure that effect directly. Instead, I think the death penalty merely serves as a marker to distinguish jurisdictions that have an effective anti-homicide political culture. The various studies, all using different standards and different assumptions, all converge on the same rough answers because many different ineptly-measured factors point in the same general direction. Metaphorically, I don’t think they can make an ordinance map of the landscape but they can determine which general direction is downhill.

Why is it important to question studies that reinforce our own beliefs? Simple, live by the study, die by the study. Undoubtedly, changing a few definitions or assumptions in future studies might give us the opposite answer. By giving credit to a flawed methodology now we force ourselves to accept any answer it gives in the future.

Still, it will be interesting to see secular-leftist opponents of the death penalty squirm their way out of this one. They pride themselves on being data-driven members of the “reality based” community. For decades they have used studies with dubious methodology to bully people who disagreed with them. Now they will have to explain why a wide range of studies all refute their ideas. Most death-penalty opponents won’t change their minds but the subsequent mental gymnastics they preform will be of Olympic quality.

Bring popcorn.