Hindsight Bias

Definition

Recollection or reevaluation of past events can be affected by what has happened since. In particular, once people know the outcome of an event, they tend to overestimate what could have been anticipated in foresight. This effect has been termed hindsight bias or the knew-it-all-along effect.

Designs, Materials, and Measures

Two different general experimental procedures are usually employed. In the memory design, people first give an (unbiased) answer, then receive the solution and are finally asked to recall their earlier, original answer. In the control situation, the same items are given to other people without providing them with the solution before they recall their original answer. In the hypothetical design, people receive the solution right away and are then asked to provide the answer they would have given without this knowledge. In the control situation, other people are asked for their answers without giving them the solution beforehand. Generally, hindsight bias is said to exist whenever the estimates made in hindsight lie closer to the solution than those made in foresight, and when the measure that captures this difference is significantly larger than for a control group.

The phenomenon is very robust across content domains. It has been found in general-knowledge questions, in political or business developments, in predictions of elections or sport results, in medical diagnoses or in personality assessment, to name only a few. It is also very robust across type of tasks. The following list is probably not exhaustive, but it covers most of the types that have been used. Hindsight bias has been found with two-alternative-forced-choice tasks, both with respect to choices and to confidence in their correctness (“Which city has more inhabitants, London or Paris?”), with confidence in the correctness of assertions (“True or false: London has more inhabitants than Paris”), with numerical questions (“How many inhabitants does London have?”), with predicting outcomes of survey questions on a percentage scale (“How many German households currently have Internet access?”), with rating the likelihoods of possible developments of a given scenario (e.g., outcomes of international conflicts, patient histories, or consequences of business decisions) or with answers on closed rating scales using a few categories (e.g., rating one's own or someone else's performance, school grade, satisfaction or personality traits).

The most common measures in the memory design compare preand post-outcome estimates with respect to their distance to the solution (in the hypothetical design, pre-outcome and post-outcome estimates are obtained between-subjects). If the task requires an answer on a limited scale (e.g., a dichotomous choice or an answer on a percentage scale), the measure can be simplified by more or less directly comparing the responses given in foresight and those given in hindsight. The memory design involves repeated measurement; therefore, one can and should, in addition, determine the proportion of correct recollections. Because correct recollections have a bias of zero and thus diminish the overall effect, they may contribute to the finding that hindsight bias is typically smaller in the memory than in the hypothetical design.

Relevance, Related Phenomena, and Theoretical Accounts

Hindsight bias is one of the most frequently cited cognitive biases. It possesses relevance for theories about memory storage and retrieval of information but has several practical implications as well. Consider, for example, a physician who, knowing the diagnosis a colleague has made, is asked for a second opinion. Or consider a researcher who is asked to review a manuscript but knows the opinion of another reviewer. Many studies have shown that the new and allegedly independent judgements are most likely biased toward those that are already available. In other words, second judgments are less independent from previous ones than one would like to think. Moreover, feeling wiser in hindsight could also lead people to wrong [Page 431]predictions of how they would have reacted in that situation (i.e., without the knowledge of how things would turn out). For example, having understood why the Space Shuttle Challenger disaster occurred may affect one's evaluations of the people involved and their omissions and commissions.

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