Cross-state and time-series comparisons of death penalty effects suffer from uncontrolled concurrent social factors.

Evidence

Homicide rates were compared in neighboring states with and without capital punishment, such as Illinois, which at one point imposed the death penalty, and Michigan, which does not. The validity of this method depends on how well matched executing and nonexecuting states are for factors that affect murder rates. A second approach relies on time-series analyses. Societies impose, abolish, and reinstate the death penalty for capital crimes. Time-series data are analyzed to ascertain whether adoption of the death penalty reduces murder rates and whether its abolition is accompanied by a rise in murders. However, the interpretation of changes in murder rates over time is complicated by the fact that a host of social factors that can affect homicide rates change concurrently. — Albert Bandura, Moral Disengagement, 1945

Categorization

• corroborated: 2 independent passages support this claim — Albert Bandura, Moral Disengagement: How People Do Harm…, 1945