Attempts to Debias Hindsight Backfire!

byGram_Stone3y13th Jun 20169 comments

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(Content note: A common suggestion for debiasing hindsight: try to think of many alternative historical outcomes. But thinking of too many examples can actually make hindsight bias worse.)

Followup to: Availability Heuristic Considered Ambiguous

Related to: Hindsight Bias

I.

Hindsight bias is when people who know the answer vastly overestimate its predictability or obviousness, compared to the estimates of subjects who must guess without advance knowledge.  Hindsight bias is sometimes called the I-knew-it-all-along effect.

The way that this bias is usually explained is via the availability of outcome-related knowledge. The outcome is very salient, but the possible alternatives are not, so the probability that people claim they would have assigned to an event that has already happened gets jacked up. It's also known that knowing about hindsight bias and trying to adjust for it consciously doesn't eliminate it.

This means that most attempts at debiasing focus on making alternative outcomes more salient. One is encouraged to recall other ways that things could have happened. Even this merely attenuates the hindsight bias, and does not eliminate it (Koriat, Lichtenstein, & Fischhoff, 1980; Slovic & Fischhoff, 1977).

II.

Remember what happened with the availability heuristic when we varied the number of examples that subjects had to recall? Crazy things happened because of the phenomenal experience of difficulty that recalling more examples caused within the subjects.

You might imagine that, if you recalled too many examples, you could actually make the hindsight bias worse, because if subjects experience alternative outcomes as difficult to generate, then they'll consider the alternatives less likely, and not more.

Relatedly, Sanna, Schwarz, and Stocker (2002, Experiment 2) presented participants with a description of the British–Gurkha War (taken from Fischhoff, 1975; you should remember this one). Depending on conditions, subjects were told either that the British or the Gurkha had won the war, or were given no outcome information. Afterwards, they were asked, “If we hadn’t already told you who had won, what would you have thought the probability of the British (Gurkhas, respectively) winning would be?”, and asked to give a probability in the form of a percentage.

Like in the original hindsight bias studies, subjects with outcome knowledge assigned a higher probability to the known outcome than subjects in the group with no outcome knowledge. (Median probability of 58.2% in the group with outcome knowledge, and 48.3% in the group without outcome knowledge.)

Some subjects, however, were asked to generate either 2 or 10 thoughts about how the outcome could have been different. Thinking of 2 alternative outcomes slightly attenuated hindsight bias (median down to 54.3%), but asking subjects to think of 10 alternative outcomes went horribly, horribly awry, increasing the subjects' median probability for the 'known' outcome all the way up to 68.0%!

It looks like we should be extremely careful when we try to retrieve counterexamples to claims that we believe. If we're too hard on ourselves and fail to take this effect into account, then we can make ourselves even more biased than we would have been if we had done nothing at all.

III.

But it doesn't end there.

Like in the availability experiments before this, we can discount the informational value of the experience of difficulty when generating examples of alternative historical outcomes. Then the subjects would make their judgment based on the number of thoughts instead of the experience of difficulty.

Just before the 2000 U.S. presidential elections, Sanna et al. (2002, Experiment 4) asked subjects to predict the percentage of the popular vote the major candidates would receive. (They had to wait a little longer than they expected for the results.)

Later, they were asked to recall what their predictions were.

Control group subjects who listed no alternative thoughts replicated previous results on the hindsight bias.

Experimental group subjects who listed 12 alternative thoughts experienced difficulty and their hindsight bias wasn't made any better, but it didn't get worse either.

(It seems the reason it didn't get worse is because everyone thought Gore was going to win before the election, and for the hindsight bias to get worse, the subjects would have to incorrectly recall that they predicted a Bush victory.)

Other experimental group subjects listed 12 alternative thoughts and were also made to attribute their phenomenal experience of difficulty to lack of domain knowledge, via the question: "We realize that this was an extremely difficult task that only people with a good knowledge of politics may be able to complete. As background information, may we therefore ask you how knowledgeable you are about politics?" They were then made to provide a rating of their political expertise and to recall their predictions.

Because they discounted the relevance of the difficulty of recalling 12 alternative thoughts, attributing it to their lack of political domain knowledge, thinking of 12 ways that Gore could have won introduced a bias in the opposite direction! They recalled their original predictions for a Gore victory as even more confident than they actually, originally were.

We really are doomed.


Fischhoff, B. (1975). Hindsight is not equal to foresight: the effect of outcome knowledge on judgment under uncertainty. Journal of Experimental Psychology: Human Perception and Performance, 1, 288–299.

Koriat, A., Lichtenstein, S., & Fischhoff, B. (1980). Reasons for confidence. Journal of Experimental Psychology: Human Learning and Memory, 6, 107–118.

Sanna, L. J., Schwarz, N., & Stocker, S. L. (2002). When debiasing backfires: Accessible content and accessibility experiences in debiasing hindsight through mental simulations. Journal of Experimental Psychology: Learning, Memory, and Cognition, 28, 497–502.

Slovic, P., & Fischhoff, B. (1977). On the psychology of experimental surprises. Journal of Experimental Psychology: Human Perception and Performance, 3, 544–551.

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