Adventures on the Back of the Envelope: Katz v. United States and the Popularization of the Phrase “Reasonable Expectation of Privacy”

I find it interesting how a case often is seen as standing for one thing when it’s decided, and something quite different years later. Relatedly, it can be interesting to see how courts come to glean from a decision a rule — or at least a catchphrase — that they then rely upon to decide cases before them.

I recently conducted a back-of-the-envelope exercise in this vein, sparked by a student’s question regarding the Fourth Amendment case, Katz v. United States. The gist of the student’s question was, how did the phrase “reasonable expectation of privacy” come to summarize the “was there a search” inquiry that kicks off most Fourth Amendment analysis–particularly when the phrase is found not in the majority opinion in Katz, but in Justice Harlan’s concurring opinion?

There’s a practical answer, of course, relating to the facts that (1) the next year, Terry v. Ohio parroted Harlan’s phrasing, and (2) Harlan gave courts a somewhat more workable (though still confusing) standard, or at least, framework for decision than Justice Stewart’s majority opinion did. But how quickly did courts catch on to this?

To probe this matter, working with the Westlaw ALLCASES database, I identified all state and federal cases that cited to Katz in certain subsequent years, and then, within each of these subsets, how many of these cases invoked the phrase “reasonable expectation of privacy.” The results:

1968: 3/58 (= 5%)

1969: 11/120 (=9%)

1971: 16/140 (=11%)

1973: 52/192 (=27%)

1977: 63/175 (=36%)

1981: 152/271 (=56%)

1985: 119/211 (=56%)

1989: 96/178 (=54%)

1993: 96/217 (=44%)

1997: 97/183 (=53%)

2001: 94/217 (=43%)

2005: 102/270 (=38%)

2009: 146/392 (=37%)

(I don’t know why we’ve seen a recent decline in the invocation rate for “reasonable expectation of privacy”; perhaps it has something to do with more cases being incorporated within Westlaw, perhaps something else.)

So, it looks like it took a little time–about a decade–for “reasonable expectation of privacy” to catch on as shorthand for the Katz approach. Either that, or the sorts of cases that courts heard changed over time, so as to present issues requiring resort to (or at least mention of) this test more often as the 1970s progressed. Either explanation is plausible, I suppose. One also wonders whether similar slow-burn patterns of diffusion exist in cases where a concurring opinion (in a non-Marks setting) becomes accepted as stating the governing rule.

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2 Responses

  1. Orin Kerr says:

    I’ve looked into this, too. For the decade after Katz was decided, Harlan’s test was mentioned on occasion but not expressly adopted by the Supreme Court as the test for what was a search. As far I can tel tell, the first case that clearly and unambiguously accepts Harlan’s framework as the search test is Smith v. Maryland in 1979.

    Also, it’s worth checking for “legitimate expectation of privacy” as well as “reasonable expectation of privacy,” as the former formulation has been used a lot, too, and was more common earlier on.

  2. I wonder if Scalia’s opinion in Jones, which provided an alternate to the “reasonable expectation of privacy” test, will result in a further decline in usage.