Tuesday, January 11, 2011

Did You Hear the One About the Texas Sharpshooter? (Part 21 of Cognitive Biases)

In this installment of Cognitive Biases, we'll learn why your memories get unstuck in time, why establishing hypotheses backward is a fallacy, and why we think other people always behave the same way.

Telescoping Effect

The telescoping effect is a memory bias, first documented in a 1964 article in the Journal of the American Statistical Association. People tend to perceive recent events as being more remote in time than they are (backward telescoping) and more remote events as being more recent than they are. The Galton-Crovitz test measures the effect; you can take the test here.

Texas Sharpshooter Fallacy

A sales manager I once knew had an infallible sense of what was going to sell. Because he didn’t want to waste his time, he put all his emphasis on selling what he knew would sell, and didn’t bother pushing the stuff that wouldn’t sell anyway.

This is an example of the Texas sharpshooter fallacy. The Texas sharpshooter, you see, fired a bunch of shots at the side of the barn, went over and found a cluster of hits, and drew a bullseye over them. When you don’t establish your hypothesis first and test it second, your conclusion is suspect.

This was first described in the field of epidemiology. For example, the number of cases of disease D in city C is greater than would be expected by chance. City C has a factory that has released amounts of chemical agent A into the environment. Therefore, agent A causes disease D.

Not so fast.

The cluster may be the result of chance, or there may be another cause. Now, if you conclude that agent A should be tested as a possible trigger of disease D, that’s a reasonable inference.

Finding a Nostradamus prophecy that could arguably relate to a big event in history is another example. Here’s a famous prophecy that appears to predict Hitler:

Beasts wild with hunger will cross the rivers,

The greater part of the battle will be against Hister.

He will cause great men to be dragged in a cage of iron,
When the son of Germany obeys no law.

But out of a thousand prophecies, what are the odds that none of them will relate to a real event?

Trait Ascription Bias

Trait ascription bias is the tendency for people to view themselves as relatively variable in terms of personality, behavior and mood while viewing others as much more predictable in their personal traits across different situations. This may be because our own internal states are much more observable and available to us than those of others. A similar bias on the group level is called the outgroup homogeneity bias.

The degree to which we fall into this bias often depends on how well we know the other person, but not entirely. “You always behave like that” is an accusation most of us have leveled at a loved one at some time in our lives.

More next week.

Previous Installments

You can find the bias you’re interested in by clicking in the tag cloud on the right. To find all posts concerning cognitive biases, click the very big phrase.

Part 1 — Bias blind spot, confirmation bias, déformation professionnelle, denomination effect, moral credential effect.

Part 2 — Base rate fallacy, congruence bias, experimenter’s bias

Part 3 — Ambiguity aversion effect (Ellsberg paradox), choice-supportive bias, distinction bias, contrast effect

Part 4 — Actor-observer bias, anchoring effect, attentional bias, availability cascade, belief bias

Part 5 — Clustering illusion, conjunction fallacy, cryptomnesia

Part 6 — Disposition effect, egocentric bias, endowment effect, extraordinarity bias

Part 7 — False consensus effect, false memory, Forer effect, framing, fundamental attribution error

Part 8 — Gambler’s fallacy, halo effect

Part 9 — Hawthorne effect, herd instinct, hindsight bias, hyperbolic discounting

Part 10 — Illusion of asymmetric insight, illusion of control, illusory superiority, impact bias, information bias, ingroup bias, irrational escalation

Part 11 — Just-world phenomenon, loss aversion, ludic fallacy, mere exposure effect, money illusion

Part 12 — Need for closure, neglect of probability, “not-invented-here” (NIH) syndrome, notational bias

Part 13 — Observer-expectancy effect, omission bias, optimism bias, ostrich effect, outgroup homogeneity bias, overconfidence effect

Part 14 — Pareidolia, planning fallacy, post-purchase rationalization

Part 15 — Projection bias, pseudocertainty effect, publication bias

Part 16 — Reactance, reminiscence bump, restraint bias, rosy retrospection

Part 17 — Selection bias, selective perception, self-fulfilling prophecy

Part 18 — Self-serving bias, Semmelweis reflex, serial position effect

Part 19 — Status quo bias, stereotyping, subadditivity effect

Part 20 — Subjective validation, suggestibility, system justification theory


  1. The Texas Sharpshooter Effect has also been referred to as HARKing, hypothesizing after the results are known. Investigators might have a certain hypothesis in mind when beginning a research study and decide upon a way to test that hypothesis. But once they see the data, 20-20 hindsight kicks in, and the hypothesis is often modified post hoc.

  2. Right. The only cure is to test the opposite proposition — see the Hawthorne Effect.