Over much of the last half-century, the legal and political history of the death penalty in the United States has closely paralleled the debate within social science about its efficacy as a deterrent. Sociologist Thorsten Sellin's careful comparisons of the evolution of homicide rates in contiguous states from 1920 to 1963 led to doubts about the existence of a deterrent effect caused by the imposition of the death penalty. This work likely contributed to the waning reliance on capital punishment, and executions virtually ceased in the late 1960s. In the 1972 Furman decision, the Supreme Court ruled that existing death penalty statutes were unconstitutional. In 1975, Isaac Ehrlich's analysis of national time-series data led him to claim that each execution saved eight lives. Solicitor General Robert Bork cited Ehrlich's work to the Supreme Court a year later, and the Court, while claiming not to have relied on the empirical evidence, ended the death penalty moratorium when it upheld various capital punishment statutes in Gregg v. Georgia and related cases. The injection of Ehrlich's conclusions into the legal and public policy arenas, coupled with the academic debate over Ehrlich's methods, led the National Academy of Sciences to issue a 1978 report which argued that the existing evidence in support of a deterrent effect of capital punishment was unpersuasive. Over the next two decades, as a series of academic papers continued to debate the deterrence question, the number of executions gradually increased, albeit to levels much lower than those seen in the first half of the twentieth century...