• Third, while most panel studies use very similar regression methods, time-series studies use a wide assortment of specialized time series methods.
• Fourth, the designs of time-series studies are more varied than are those of panel studies. Perhaps the most important difference among time-series studies is the number of execution events examined. Some time-series research focuses on the effect of a single execution event, and other studies combine data on many execution events and analyze their temporal association with homicide rates in a single statistical model.
The variation of research methods in the time-series studies makes it challenging to organize a cohesive discussion of the subject. It also is challenging to describe and critique the studies in a way that is understandable to audiences who do not have expertise in time-series methods. Methods for analysis of time-series data are specialized and often very technical. We address the second challenge by beginning this chapter with a nontechnical discussion of some relatively transparent problems of the studies. We then continue with further criticisms that of necessity are more technical.
Studies of single execution events attempt to identify whether a change in the homicide rate occurs in the immediate aftermath of a single execution. A decline is interpreted as evidence of deterrence; an increase is interpreted as evidence of a brutalization effect, whereby state-sanctioned executions “legitimate” homicide to some in the citizenry. If either such effect could be convincingly demonstrated, it would establish a threshold requirement for capital punishment to affect behavior, namely that “someone is seemingly listening.” However, as detailed below, the committee concluded that no existing study has successfully made such a demonstration and that the obstacles to success for a future study are formidable. As importantly, the committee concluded that a successful demonstration would have limited informational value.
Studies of a single execution event are subject to the same problem that bedevils most before-after studies. Because the execution is not conducted in the context of a carefully controlled experimental setting, other factors that affect the homicide rate may coincide with the execution event. Some event studies attempt to deal with this problem by examining changes over very short periods of time, days or a week. Although shortening the time window of observation may provide some protection from the effects of