The Deterrent Effect of Capital Punishment

In the previous chapter we examined a number of empirical studies of the supply of offences function. We now consider in more detail the specific crime of murder. In particular we examine whether or not the death penalty is an effective deterrent to the act of murder. This issue, which was once thought to be settled, has been re-opened following a particularly controversial article by Ehrlich (1975a). One of his principal conclusions was that ‘an additional execution per year over the period in question [1935–69] may have resulted, on average, in 7 or 8 fewer murders’ (p. 414). The publication of this suggested trade-off, admittedly subject to relatively large prediction errors, released a flood of criticism and comment. Many of these comments were highly technical ones aimed at Ehrlich’s data, estimation methods, choice of functional form and model specification. Others, spurred on by Ehrlich’s example, proceeded to estimate murder supply equations using different data sets. One such attempt, by Yunker (1976), produced an even more startling result — that one more execution might prevent no less than 156 murders.