Local Representativeness

The eighth graders in Indy are known to have an average IQ of 100. Fifty students have been randomly chosen to participate in a a special educational study. The first student tested has an IQ of 150. What is the average IQ expected for the 50 students

Modified from, Kahnemann, Slovic, Tversky, Judgement Under Uncertainty: Heuristics and Biases, 1982, pg 24

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Notes:

This belief in local representativeness is illustrated here in an example modified from one in Kahnemann’s book.

Ask the group to answer the question.

A common answer is that the average will be the same as it is for the whole population. That is, 100. We aren’t going to be tricked by the old gambler’s fallacy and believe that the outcome remembers the past. You know the gambler’s fallacy -- after fo