Probable Cause, Probability, and Hindsight

• Author: Chris Guthrie,Andrew J. Wistrich,Jeffrey J. Rachlinski
• Date: 01 December 2011
• DOI: http://doi.org/10.1111/j.1740-1461.2011.01230.x
• Published date: 01 December 2011

Probable Cause, Probability, and Hindsightjels_

123072..9872..98

Jeffrey J. Rachlinski, Chris Guthrie, and Andrew J. Wistrich*

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.

I. Introduction

The Fourth Amendment’s prohibition against unreasonable searches and seizures creates

a decision-making dilemma for judges.1It requires that judges supervise police investiga-

tions. The centerpiece of the Fourth Amendment’s protection of personal privacy lies in

the requirement that the police must obtain permission to conduct such searches by

obtaining a warrant from a judge.2But in the common circumstance in which an exigency

prevents a police off‌icer from obtaining a warrant, the judge must assess probable cause

*Address correspondence to Jeffrey J. Rachlinski, Professor of Law, Cornell Law School, Myron Taylor Hall, Ithaca,

NY 14853; email: jjr7@cornell.edu. 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.

1The Fourth Amendment states: “The right of the people to be secure in their persons, houses, papers, and effects,

against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable

cause, supported by Oath or aff‌irmation, and particularly describing the place to be searched, and the persons or

things to be seized.”

2Chimel v California, 395 U.S. 752, 762 (1969) (“The police must, whenever practical, obtain advance judicial

approval of searches and seizures through the warrant procedure.”); Katz v. United States, 389 U.S. 347, 357 (1967)

(“searches conducted outside the judicial process, without prior approval by judge or magistrate, are per se unrea-

sonable under the Fourth Amendment”). See William J. Stuntz, Warrants and Fourth Amendment Remedies, 77 Va.

L. Rev. 881, 882 (1991).

Journal of Empirical Legal Studies

Volume 8, Issue S1, 72–98, December 2011

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while knowing that the search was successful.3Decades of research on judgment in hind-

sight suggest that such judgments will be biased, as people cannot suppress the inf‌luence of

known outcomes on their judgments—a phenomenon known as the hindsight bias.4In this

article, we present three experiments in which we asked groups of state and federal judges

to make judgments of probable cause either in foresight or in hindsight, in hypothetical

cases. Surprisingly, we found when making probable cause determinations, judges do not

seem to be inf‌luenced by the hindsight bias.

Our result is surprising. The nature of probable cause poses a serious cognitive

challenge for judges in implementing their role as the guardians of the Fourth Amend-

ment. The cornerstone of reasonableness in searches is the concept of “probable cause.”5

Commonly, a judge will assess probable cause before the search has been conducted

because the police normally have to obtain a warrant before conducting a search. But with

numerous exceptions to the warrant requirement that arise from the inevitable exigencies

of law enforcement, the police conduct a search without obtaining a warrant.6When faced

with such an exigency, the police may avoid the need for a warrant, but they must still have

probable cause for the search.7The purpose behind allowing an exigency to exempt the

police from the warrant requirement is a practical one, but is not supposed to allow the

police to be subject to a more lenient standard of review. When searches conducted without

a warrant produce incriminating evidence to be used against a criminal defendant, the

judge must assess probable cause in full knowledge that the search uncovered incriminating

evidence. Judges must assess the facts just as if they did not know that the search uncovered

incriminating evidence. The standard remains the same, but the perspective from which

judges review a case inevitably differs in hindsight.

Judging the reasonableness of a police search in hindsight obviously places great

pressure on a judge to side with the police. A judge who refuses to issue a warrant in

foresight impedes police investigation somewhat. But concluding that a search was unrea-

sonable in hindsight, however, is apt to lead to the suppression of important evidence

against a defendant who likely committed a crime. The consequences of concluding that

3See Craig M. Bradley, Two Models of the Fourth Amendment Remedies, 83 Mich. L. Rev. 1468, 1473 (1985).

4See Baruch Fischhoff, Hindsight ⫽Foresight: The Effect of Outcome Knowledge on Judgment Under Uncertainty,

1 J. Experimental Psychol. 288 (1975) (f‌irst documenting the hindsight bias); Jeffrey J. Rachlinski, A Positive

Psychological Theory of Judging in Hindsight, 65 U. Chi. L. Rev. 571, 576–88 (1998) (reviewing the research on the

hindsight bias).

5See Wayne R. LaFave, Jerold Israel & Nancy King, Criminal Procedure 144–45 (4th ed. 2004) (arguing that probable

cause determinations are central to the Fourth Amendment); but see Andrew E. Taslitz, Margaret L. Paris & Lensee

Herbert, Constitutional Criminal Procedure 186–97 (4th ed. 2010) (showing a central role for probable cause, but

expressing concern about numerous exceptions).

6See Bradley, supra note 3, at 1473–74 (cataloging numerous exceptions to the warrant requirement); Donald L. Beci,

Fidelity to the Warrant Clause: Using Magistrates, Incentives, and Telecommunications Technology to Reinvigorate

Fourth Amendment Jurisprudence, 73 Denver U.L. Rev. 293, 295 (1996) (arguing that the exceptions to the warrant

requirement have swallowed the rule).

7LaFave et al., supra note 5, at 144–45.

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