Hindsight Devalues Science

by Eliezer Yudkowsky2 min read17th Aug 200740 comments


Hindsight BiasFallaciesHeuristics & Biases

This essay is closely based on an excerpt from Meyers’s Exploring Social Psychology ; the excerpt is worth reading in its entirety.

Cullen Murphy, editor of The Atlantic, said that the social sciences turn up “no ideas or conclusions that can’t be found in [any] encyclopedia of quotations . . . Day after day social scientists go out into the world. Day after day they discover that people’s behavior is pretty much what you’d expect.”

Of course, the “expectation” is all hindsight. (Hindsight bias: Subjects who know the actual answer to a question assign much higher probabilities they “would have” guessed for that answer, compared to subjects who must guess without knowing the answer.)

The historian Arthur Schlesinger, Jr. dismissed scientific studies of World War II soldiers’ experiences as “ponderous demonstrations” of common sense. For example:

1. Better educated soldiers suffered more adjustment problems than less educated soldiers. (Intellectuals were less prepared for battle stresses than street-smart people.) 2. Southern soldiers coped better with the hot South Sea Island climate than Northern soldiers. (Southerners are more accustomed to hot weather.) 3. White privates were more eager to be promoted to noncommissioned officers than Black privates. (Years of oppression take a toll on achievement motivation.) 4. Southern Blacks preferred Southern to Northern White officers. (Southern officers were more experienced and skilled in interacting with Blacks.) 5. As long as the fighting continued, soldiers were more eager to return home than after the war ended. (During the fighting, soldiers knew they were in mortal danger.)

How many of these findings do you think you could have predicted in advance? Three out of five? Four out of five? Are there any cases where you would have predicted the opposite—where your model takes a hit? Take a moment to think before continuing . . .

. . .

In this demonstration (from Paul Lazarsfeld by way of Meyers), all of the findings above are the opposite of what was actually found.1 How many times did you think your model took a hit? How many times did you admit you would have been wrong? That’s how good your model really was. The measure of your strength as a rationalist is your ability to be more confused by fiction than by reality.

Unless, of course, I reversed the results again. What do you think?

Do your thought processes at this point, where you really don’t know the answer, feel different from the thought processes you used to rationalize either side of the “known” answer?

Daphna Baratz exposed college students to pairs of supposed findings, one true (“In prosperous times people spend a larger portion of their income than during a recession”) and one the truth’s opposite.2 In both sides of the pair, students rated the supposed finding as what they “would have predicted.” Perfectly standard hindsight bias.

Which leads people to think they have no need for science, because they “could have predicted” that.

(Just as you would expect, right?)

Hindsight will lead us to systematically undervalue the surprisingness of scientific findings, especially the discoveries we understand —the ones that seem real to us, the ones we can retrofit into our models of the world. If you understand neurology or physics and read news in that topic, then you probably underestimate the surprisingness of findings in those fields too. This unfairly devalues the contribution of the researchers; and worse, will prevent you from noticing when you are seeing evidence that doesn’t fit what you really would have expected.

We need to make a conscious effort to be shocked enough.

1 Paul F. Lazarsfeld, “The American Solidier—An Expository Review,” Public Opinion Quarterly 13, no. 3 (1949): 377–404 .

2 Daphna Baratz, How Justified Is the “Obvious” Reaction? (Stanford University, 1983) .