Execution and Deterrence

November 20, 2007
Posted by Jay Livingston

The Sunday New York Times had a front page article about recent studies showing that the death penalty deters murder. The studies, nearly all done by economists, give estimates of between 3 and 18 lives saved for each person executed.

The main critique of these studies argues that the small number of executions makes it impossible to draw solid conclusions. Last year, for example, Arizona had no executions; this year, Arizona executed one person. A change of 3 or even 18 murders in the next year, would probably fall within the range of random change.

In many areas of life, it makes sense to play the percentages. You send a left-handed batter against a right-handed pitcher. Even if the strategy doesn’t work this time, there’s no great consequence, and it will work in the long run thanks to the “law of large numbers” (what most people know as the “law of averages”). But , as the name says, that law is enforced only when the numbers are large. Do we want the numbers of executions to be that large?

Personally, when it comes to killing prisoners, I’d prefer a demonstration of deterrence that works with small numbers. I want to see a clearer link between cause and effect. Ideally, we would have evidence of at least three actual Arizonans (preferably 18) who were deterred by that execution. But of course we don’t have such evidence. All we have are estimates from complicated multiple regressions based on decades of data.

I don’t have the data sets or the statistical skills to do these regressions, so I did my own quick and dirty, highly nonscientific analysis of a couple of states – Texas and Oklahoma. In 1996, for example, the number of executions in Texas dropped from 19 to 3. The number of murders should have skyrocketed. But the next year, the number of murders decreased by 150 (from 1477 to 1327).

Then W. and Alberto got back to work, and in 1997, executions went from 3 to 37. Let’s see, at 10 saved lives per execution, murder in the next year should have been down by at least three hundred. But in fact, the next year, there were 20 more murders.

The numbers from Oklahoma, which started emulating its neighbor to the south, are similarly inconclusive. In 2000, it increased executions by 5 (from 6 to 11). Were there fifty or even fifteen fewer murders the next year? No, the number went from 182 to 185.

Yes, my method (or is it my methodolgy?) stinks. Its estimate of lag time is crude. It leaves out all those other factors that might affect murder rates, and it ignores the aggregate data. But when it comes to the state taking lives, I’m inclined to demand something that works every time, not just “in general.”

The economists’ formulations also leave out something important – a model of just how deterrence works. They simply make the standard economic assumption that raising the cost of something lowers demand. If you raise the cost of committing murder, fewer people will be willing to pay that price.

But before I accept the idea that deciding whether to kill someone is like deciding whether to buy a new car, I’d like to see some street-level evidence.

Finally, none of this speaks to other issues raised in the Times article and in the letters responding to it – the costs (especially relative to other anti-crime policies), the morality, and the risk of executing the innocent.