Deterrence in the Twenty-first Century: A Review of the Evidence

The evidence in support of the deterrent effect of the certainty of punishment is far more consistent than that for the severity of punishment. However, the evidence in support of certainty’s effect pertains almost exclusively to apprehension probability. Consequently, the more precise statement is that certainty of apprehension, not the severity of the ensuing legal consequence, is the more effective deterrent. This conclusion has important policy implications among which are that lengthy prison sentences and mandatory minimum sentencing cannot be justified on deterrence. There are four major research gaps. The first concerns the mechanism by which police affect perceptions of the probability of apprehension. The second concerns the inextricable link between the deterrent effect of the threat of punishment and the potentially criminogenic effect of the experience of punishment. The third concerns the concept of a sanction regime defined by the sanctions legally available and how that legal authority is administered. Theories of deterrence conceive of sanctions in the singular not the plural and do not provide a conceptual basis for considering the differential deterrent effects of different components of the sanction regime. The fourth involves sanction risk perceptions. Establishing the link between risk perceptions and sanction regimes is imperative; unless perceptions adjust, however crudely, to changes in the sanction regime, desired deterrent effects will not be achieved.