Supreme Court Appointments as a Poisson Distribution

Abstract

When Jimmy Carter stepped down as president on January 20, 1981, he carried with him at least one unique distinction: he is the only president serving four or more years who failed to make a single appointment to the U.S. Supreme Court. Since four-year presidents have appointed as many as five justices in a term and have averaged approximately two such appointments,' the Carter experience may be seen by some as anomalous. This is particularly true if one thinks the age and health of the Court's justices at the beginning of a presidency are predictors of the appointments to be made over the following four years,2 or if one views the appointments themselves as interdependent events. From a different perspective, one may view the vacancies occurring in the Court as a series of independent events that distribute themselves across time according to some statistical function. After Franklin D. Roosevelt was unable to make any Court appointments in his first term, W. Allen Wallis (1936) established that, on a yearly basis, the frequency of vacancies was accurately described by a Poisson function.3 The Wallis analysis covered the period 1837-1932, finding a significant fit between a Poisson distribution of vacancies and the distribution of the actual va-