The Role of Probability of Detection in Judgments of Punishment

In nine experiments — one a questionnaire given to Israeli judges, the rest on the World Wide Web — we examined the effect of probability of detection of an offense on judgments of punishment. When cases differing in probability were separated, we found almost no evidence for attention to probability (as found previously by others). When cases were presented next to each other, however, a substantial minority of subjects took probability into account. Attention to probability was increased in one study by a probe manipulation concerning deterrent effects. We found inconsistent effects of identifying the perpetrator, or of asking subjects to consider policies versus individuals. Some subjects thought that it was unfair to consider probability, but more subjects thought that probability was relevant because of the need for deterrence. We suggest that the failure to consider probability is to some extent an example of the “isolation effect,” in which people do not think much about secondary effects, rather than entirely a result of ideological commitment to a “just desserts” view of punishment. “To enable the value of the punishment to outweigh that of the profit of the offense, it must be increased, in point of magnitude, in proportion as it falls short in point of certainty.” (Bentham, 1948/1843, Ch. 14, section XVIII).