Thinking, Fast and Slow - Daniel Kahneman

epresentativeness when we judge the potential leadership of a candidate for office by the
shape of his chin or the forcefulness of his speeches.
Although it is common, prediction by representativeness is not statistically optimal. Michael
Lewis’s bestselling Moneyball is a story about the inefficiency of this mode of prediction.
Professional baseball scouts traditionally forecast the success of possible players in part by
their build and look. The hero of Lewis’s book is Billy Beane, the manager of the Oakland A’s,
who made the unpopular decision to overrule his scouts and to select players by the statistics of
past performance. The players the A’s picked were inexpensive, because other teams had
rejected them for not looking the part. The team soon achieved excellent results at low cost.
The Sins of Representativeness
Judging probability byals representativeness has important virtues: the intuitive impressions
that it produces are often—indeed, usually—more accurate than chance guesses would be.
On most occasions, people who act friendly are in fact friendly.
A professional athlete who is very tall and thin is much more likely to play basketball
than football.
People with a PhD are more likely to subscribe to The New York Times than people who
ended their education after high school.
Young men are more likely than elderly women to drive aggressively.
In all these cases and in many others, there is some truth to the stereotypes that govern
judgments of representativeness, and predictions that follow this heuristic may be accurate. In
other situations, the stereotypes are false and the representativeness heuristic will mislead,
especially if it causes people to neglect base-rate information that points in another direction.
Even when the heuristic has some validity, exclusive reliance on it is associated with grave
sins against statistical logic.
One sin of representativeness is an excessive willingness to predict the occurrence of
unlikely (low base-rate) events. Here is an example: you see a person reading The New York
Times on the New York subway. Which of the following is a better bet about the reading
stranger?