PREDICTING SUPREME COURT CASES PROBABILISTICALLY: THE SEARCH AND SEIZURE CASES, 1962-1981

The Fourth Amendment, which protects against unreasonable searches and seizures, is "one of the laws most vital to our liberty" (Amsterdam, 1974:377). Yet we are still not sure what makes a particular action by the government an unreasonable search or seizure. According to Dworkin (1973), the search and seizure cases are "a mess" (p. 329).

It was felt that our incomprehension of the Fourth Amendment cases was not a result of the decisions themselves, but the manner in which the decisions were studied. Previous quantitative attempts to explain court decisions lacked any theoretical base and used methods that were rather inappropriate. Qualitative attempts to explain court decisions place an overreliance on precedent, and either have too many exceptions or unwieldy classification.

In order to attack this problem a theoretical model of Supreme Court decision making was developed that assumes members of the Court are satisficers who monitor certain facts from the lower court's opinion. These facts strongly predispose the members towards finding a search reasonable or unreasonable. The model was tested using the facts of the case, such as whether there was a warrant or probable cause, as the independent variables. The decisions of the Court and the individual justices as to the reasonableness of the search or seizure were the dependent variables. The data were the Supreme Court's search and seizure decisions from the Fall of 1962 until the Spring of 1981. The parameters were estimated by the multivariate technique probit.

The model predicted 76% of the Court's decisions correctly and explained 57% of the variance in those decisions. The point estimates were almost universally in the right direction, of the expected relative magnitude and statistically significant. The place of the search, the extent of the intrusion, the existence of a warrant, a few mitigating circumstances, the presence of the United States as a party and the particular makeup of the Court were all found to be important variables. The results from the justices were fairly consistent with those of the Court itself, but many of the estimates failed to attain statistical significance.