Capital Punishment and Capital Murder: Market Share and the Deterrent Effects of the Death Penalty

All of the recent studies claiming a relationship between death penalty policy and homicide rates suffer from an important and avoidable aggregation error: they examine the relationship between death penalty variables and total non-negligent homicide rates, despite the fact that three-fourths of all such killings do not meet the statutory criteria to be eligible for the death penalty. This study isolated the quarter of all killings that might qualify for death and used trends in these killings to test for marginal deterrent impact of death penalty policy. An effective death penalty would produce changes in this category of homicides: the market share of all homicide that are death-eligible should decline in the face of the threat of execution. But that is not the case. The authors' search for death penalty deterrence where it should be a strong influence on homicide rates has produced consistent results: the marginal deterrent effect of the threat or example of execution on those cases at risk for such punishment is invisible.