As discussed in Chapter 2none of these successive stages in processing through the criminal justice system is certain. For obvious reasons, it is not possible to conduct a randomized capital punishment experiment.
In an experiment, the differences between the sanction regimes in the treatment and control jurisdictions would define what constitutes treatment.
Abstract Executions in Texas from — do not deter homicides, contrary to the results of Land et al. Across the social science disciplines, the concepts of certainty and severity have been made operational in deterrence research in very different ways. Instead, it is a lengthy prison sentence—often life without the possibility of parole.
Consider an actual, not hypothetical, example. There must also be some possibility that the sanction will be incurred if the crime is committed. It is a truism that sanction threats cannot deter unless at least some would-be offenders are aware of the threat.
Thus, providing the legal authority for the use of the death penalty for a special class of murders might prevent murders of that type by making clear that these types of murder are deemed particularly heinous.
Such conclusions however are highly sensitive to model specification decisions, calling into question the assumptions about fixed parameters and constant structural relationships.
The remainder of this chapter lays out key challenges to estimating the causal effect of capital punishment on murder rates. Some degree of deterrence only requires that some people who are actively considering committing a crime are aware of the penalties and that their behavior is influenced by this awareness.
However, if deterrence is predicated on the perception of the risk of execution, short-term or even longer term variations in the rate of executions may not produce changes in the homicide rate, even if the death penalty is a deterrent.
Instead, it would test a particular capital punishment against a specific alternative regime without capital punishment.