Streetlight effect

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Bias from searching only where it is easy

title: "Streetlight effect" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["scientific-observation", "metaphors"] description: "Bias from searching only where it is easy" topic_path: "general/scientific-observation" source: "https://en.wikipedia.org/wiki/Streetlight_effect" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Bias from searching only where it is easy ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/a/af/Lamppost_and_tree.jpg" caption="It is harder to find something on the part of the ground that is not well lit." alt="A lamp lighting a small portion of a dark snowy area."] ::

The streetlight effect, or the drunkard's search principle, is a type of observational bias that occurs when people only search for something where it is easiest to look. Both names refer to a well-known joke:

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The anecdote appears in a story of the Islamic folklore character Nasreddin. In an undated Persian version of the story, Nasreddin loses a ring in a dark room of his house but instead looks for it in the yard because there is "much more light" out there. According to Idries Shah, this tale is used by many Sufis, commenting upon people who seek exotic sources for enlightenment.

The version with a drunk under a streetlight goes back at least to the 1920s, and has been used metaphorically in the social sciences since at least 1964, when Abraham Kaplan referred to it as "the principle of the drunkard's search". Noam Chomsky has used the tale as a picture of how science operates: "Science is a bit like the joke about the drunk who is looking under a lamppost for a key that he has lost on the other side of the street, because that's where the light is. It has no other choice."

References

References

  1. David H. Freedman. (August 1, 2010). ["The Streetlight Effect"](http://discovermagazine.com/2010/jul-aug/29-why-scientific-studies-often-wrong-streetlight-effect }}
    - [[:wikibooks:Sufism/Nasrudin). [[Discover (magazine).
  2. David H. Freedman. (2010). "Wrong: Why Experts Keep Failing Us". [[Little, Brown and Company]].
  3. (11 April 2013). ""Did You Lose the Keys Here?" "No, But the Light Is Much Better Here"".
  4. Shah, Idries. (1964). "The Sufis". Doubleday.
  5. United States Senate Committee on Military Affairs. (December 1960). "Bulletin of the Atomic Scientists". Educational Foundation for Nuclear Science, Inc..
  6. Kaplan, Abraham. (1964). "The Conduct of Inquiry: Methodology for Behavioral Science". Transaction Publishers.
  7. Barsky, Robert F.. (1998). "Noam Chomsky: a life of dissent". MIT Press.

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