Posted by Eugene Volokh:
Cass Sunstein & Adrian Vermeule for the Death Penalty:
Their essay is [1]available for download here; here's the abstract
(paragraph breaks added):
Recent evidence suggests that capital punishment may have a
significant deterrent effect, preventing as many as eighteen or
more murders for each execution. This evidence greatly unsettles
moral objections to the death penalty, because it suggests that a
refusal to impose that penalty condemns numerous innocent people to
death.
Capital punishment thus presents a life-life tradeoff, and a
serious commitment to the sanctity of human life may well compel,
rather than forbid, that form of punishment. Moral objections to
the death penalty frequently depend on a distinction between acts
and omissions, but that distinction is misleading in this context,
because government is a special kind of moral agent.
The familiar problems with capital punishment -� potential error,
irreversibility, arbitrariness, and racial skew -� do not argue in
favor of abolition, because the world of homicide suffers from
those same problems in even more acute form. The widespread failure
to appreciate the life-life tradeoffs involved in capital
punishment may depend on cognitive processes that fail to treat
�statistical lives� with the seriousness that they deserve.
I've read the paper, and though I don't entirely agree with all the
analysis in it, I think it makes some very important points, and will
attract a lot of attention. What most intrigued me, incidentally, was
its summary of the recent deterrence studies, which I hadn't known
about. (I support the death penalty on retributive grounds, but
obviously if it's a powerful deterrent, that would reinforce the
retributivists' support and may also bring around many
nonretributivists.) Here's their summary of the evidence; for
footnotes, please see the paper itself:
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 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.
In the period between 1972 and 1976, the Supreme Court produced an
effective moratorium on capital punishment, and an extensive study
exploits that fact to estimate the deterrent effect. Using
state-level data from 1960-2000, the authors make before-and-after
comparisons, focusing on the murder rate in each state before and
after the death penalty was suspended and reinstated. The authors
find a substantial deterrent effect. After suspending the death
penalty, 91% of states faced an increase in homicides � and in 67%
of states, the rate was decreased after reinstatement of capital
punishment.
A recent study offers more refined findings. Disaggregating the
data on a state by state basis, Joanna Shepherd finds that the
nation-wide deterrent effect of capital punishment is entirely
driven by only six states -- and that no deterrent effect can be
found in the twenty-one other states that have restored capital
punishment. What distinguishes the six from the twenty-one? The
answer lies in the fact that states showing a deterrent effect are
executing more people than states that do not. 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.
All in all, the recent evidence of a deterrent effect from capital
punishment seems impressive. But in studies of this kind, it is
hard to control for confounding variables, and a degree of doubt
inevitably remains. It remains possible that these findings will be
exposed as statistical artifacts or will be found to rest on flawed
econometric methods. More broadly, skeptics are likely to question
the mechanisms by which capital punishment has a deterrent effect.
On the skeptical view, many murderers lack a clear sense of the
likelihood and perhaps even the existence of executions in their
state; further problems for the deterrence claim are introduced by
the fact that capital punishment is imposed infrequently and after
long delays. In any case many murders are committed in a passionate
state that does not lend itself to an all-things-considered
analysis on the part of perpetrators.
As mentioned above, and as we discuss in Part IV, these
suppositions are in some tension with existing evidence. But let us
suppose that these doubts are reasonable. If so, should current
findings be deemed irrelevant for purposes of policy and law? That
would be an odd conclusion. In regulation as a whole, it is common
to embrace some version of the Precautionary Principle -� the idea
that steps should be taken to prevent significant harm even if
cause-and-effect relationships remain unclear and even if the risk
is not likely to come to fruition. Even if we reject strong
versions of the Precautionary Principle, it hardly seems sensible
that governments should ignore evidence demonstrating a significant
possibility that a certain step will save large numbers of innocent
lives.
For capital punishment, critics often seem to assume that evidence
on deterrent effects should be ignored if reasonable questions can
be raised about it. But as a general rule, this is implausible. In
most contexts, the existence of reasonable questions is hardly an
adequate reason to ignore evidence of severe harm. If it were, many
environmental controls would be in serious jeopardy. We do not mean
to suggest that government should commit what many people consider
to be, prima facie, a serious moral wrong simply on the basis of
speculation that this step will do some good. But a degree of
reasonable doubt does not seem sufficient to doom capital
punishment, if the evidence suggests that significant deterrence
occurs.
In any event, as they say, read the whole thing -- and, better yet,
also read the studies it cites (something I plan to do shortly).
References
1. http://aei-brookings.org/publications/abstract.php?pid=922
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