When I went to law school, my criminology lecturer Gordon Hawkins taught us that research clearly showed that the death penalty had no measurable deterrent effect on murder/crime rates. But I recall thinking at the time that the evidence he cited didn’t sound all that compelling. It consisted mostly of anecdotes about how the incidence of pickpocketing in 18th century England was highest at Newgate among crowds watching convicted pickpockets being hung. A colourful story, I thought, but hardly enough to ground a scientific conclusion about the deterrent efficacy of a particular punishment.
Now a recent article (so far unpublished but downloadable from SSRN) by noted US legal academics Cass R. Sunstein and Adrian Vermeule suggests that my youthful intuition might have been correct. Sunstein and Vermeule make the somewhat startling claim that governments may be under a moral duty to legislate for the death penalty! Before simply dismissing this as yet another piece of fascistic nonsense on a par with the recent pseudo-academic apologia for torture by Australia’s Mirko Bagaric and Julie Clarke, readers would be well advised to note that Sunstein and Vermeule’s article is strongly based in a series of econometric studies of US crime figures (not that economists are necessarily any more immune from writing egregious nonsense than lawyers):
For many years, the deterrent effect of capital punishment was sharply disputed. But a great deal of recent evidence strengthens the claim that capital punishment has large deterrent effects. The reason for the shift is that a wave of sophisticated econometric studies have exploited a newly-available form of data, so-called “panel data” that uses all information from a set of units (states or counties) and follows that data over an extended period of time. A leading study [by Dezhbakhsh et al] used county-level panel data from 3,054 U.S. counties between 1977 and 1996. The authors find that the murder rate is significantly reduced by both death sentences and executions. The most striking finding is that on average, each execution results in 18 fewer murders.
Other econometric studies also find a substantial deterrent effect. In two papers, Paul Zimmerman uses state-level panel data from 1978 onwards to measure the deterrent effect of execution rates and execution methods. He estimates that each execution deters an average of fourteen murders. Using state-level data from 1977 to 1997, Mocan and Gittings find that each execution deters five murders on average. They also find that increases in the murder rate come from removing people from death row and also from commutations in death sentences. Yet another study, based on state-level data from 1997- 1999, finds that a death sentence deters 4.5 murders and an execution deters three murders. The same study investigates the question whether executions deter crimes of passion and murders by intimates. The answer is clear: these categories of murder are deterred by capital punishment. 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.
As a result of these studies, Sunsten and Vermeule argue:
If the current evidence is even roughly correct, then a refusal to impose capital punishment will effectively condemn numerous innocent people to death. States that choose life imprisonment, when they might choose capital punishment, are ensuring the deaths of a large number of innocent people. On moral grounds, a choice that effectively condemns large numbers of people to death seems objectionable to say the least. For those who are inclined to be skeptical of capital punishment for moral reasons¢â¬âa group that includes one of the current authors¢â¬âthe task is to consider the possibility that the failure to impose capital punishment is, prima facie and all things considered, a serious moral wrong. …
As an empirical matter, criminal law is pervaded by its own risk-risk tradeoffs. If the deterrent signal works, a failure to impose stringent penalties on certain crimes will increase the number of those crimes. A refusal to impose such penalties is, for that reason, problematic from the moral point of view. The very idea of “equal protection of the laws,” in its oldest and most literal sense, attests to the importance of enforcing the criminal and civil law so as to safeguard the potential victims of private violence. What we are suggesting is that the death penalty produces a risk-risk tradeoff of its own, indeed what we will call a life-life tradeoff, to the extent that a refusal to impose capital punishment yields a significant increase in the number of deaths of innocent people.
Of course this point does not resolve the capital punishment debate. By itself, the act of execution may be a wrong, in a way that cannot be said for an act of imposing civil or criminal penalties on (say) environmental degradation. But the existence of life-life tradeoffs raises the possibility that for those who oppose killing, a rejection of capital punishment is not necessarily mandated. On the contrary, it may well be morally compelled. At the very least, those who object to capital punishment, and do so in the name of protecting life, must come to terms with the fact that the failure to inflict capital punishment might fail to protect life¢â¬âand must, in our view, justify their position in ways that do not rely on question-begging claims about the distinction between acts and omissions.
I have always opposed the death penalty on a range of grounds, including fundamental moral ones as well as utilitarian calculations about deterrence and the like. But perhaps it isn’t an overwhelmingly obvious moral conclusion that legalised cold-blooded killing of another human being should be regarded as fundamentally morally abhorrent and always wrong, if by failing to impose the death penalty we condemn 18 (or even 5) innocent if anonymous people to death.
The other argument against the death penalty that I have always seen as persuasive lies in its irreversibility: what if we’re wrong and the convicted person was really innocent (e.g. Lindy Chamberlain)? Then there’s the sometime arbitrariness of imposition of the death penalty, not to mention American evidence of a racial bias: blacks are more likely than whites to be sentenced to death. But Sunstein and Vermeule also have an answer to this argument:
Once the act-omission distinction is no longer central, it becomes clear that the standard moral objections to capital punishment apply even more powerfully to the murders that capital punishment prevents. Those murders also cause irreversible deaths: the deaths of the victims of murder. Private murders are also often highly arbitrary, involving selectivity on any number of morally irrelevant or objectionable grounds. African-Americans, for example, are far more likely than other groups to be the victims of murder. In 2003, 48% of murder victims were white and 48% were African-American¢â¬âmeaning that the racial disparity in the probability of becoming a murder victim is even greater than the racial disparity in the probability of ending up on death row. An important corollary is that the benefits of capital punishment, to the extent that it operates as a powerful deterrent of murder, are likely to flow disproportionately to African-Americans.
Sunstein and Vermeule also observe that there seems to be a threshold number of executions below which no deterrent effect occurs:
In fact the data show a “threshold effect”: deterrence is found in states that had at least nine executions between 1977 and 1996. In states below that threshold, no deterrence can be found. This finding is intuitively plausible. Unless executions reach a certain level, murderers may act as if the death is so improbable as not to be worthy of concern. Her main lesson is that once the level of executions reaches a certain level, the deterrent effect of capital punishment is substantial.
So it isn’t enough merely to legislate for the death penalty, it has to be imposed and inflicted often enough to remind potential murderers of the likely consequences of their actions.
I have to confess that my moral intuition still tells me that the death penalty is barbaric and wrong, but I’m not prepared to dismiss Sunstein and Vermeule’s arguments, or the econometric evidence on which they’re based, out of hand. What do readers think?
PS – As usual, Wikipedia has an excellent article on capital punishment, with lots of links and a good summary of the arguments for and against the death penalty.