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Probable Cause, Probability, and Hindsight


Jeffrey J. Rachlinski, Professor of Law, Cornell Law School, Myron Taylor Hall, Ithaca, NY 14853; email: Guthrie is Dean and John Wade-Kent Syverud Professor of Law, Vanderbilt University Law School; Wistrich is Magistrate Judge, U.S. District Court, Central District of California.


When judges assess probable cause, they must do so either in foresight (when determining whether to issue a warrant) or in hindsight (when determining whether to allow the admission of evidence obtained without a search warrant). Although the legal standard for probable cause is the same, and the facts that might support cause are the same, judges who assess probable cause in hindsight invariably know whether a search produced incriminating evidence or not. Research on the hindsight bias suggests that judges will be unable to set aside this knowledge and judge probable cause as if they were working in foresight. In this article, we present three experiments in which we asked 900 state and federal judges to make judgments of probable cause either in foresight or in hindsight, in hypothetical cases. Surprisingly, we found that that judges make similar rulings on probable cause in foresight and in hindsight. We also found that hindsight appears to cloud judges' abilities to assess the likely outcome of the search, but hindsight does not influence their legal judgments.