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representativeness error

Most important human judgments are made under conditions of uncertainty. We use heuristics, or rules of thumb, to guide us in such instances as we try to determine what belief or action has the highest probability of being the correct one in a given situation. Social psychologists such as Thomas Gilovich, Daniel Kahneman, and Amos Tversky have studied several important heuristics and discovered errors associated with their use. One of these heuristics is the representativeness heuristic. In judging items, we compare them to a prototype or representative idea and tend to see them as typical or atypical according to how they match up with our model.

The problem with the representativeness heuristic is that what appears typical sometimes blinds you to possibilities that contradict the prototype. Jerome Groopman, M.D. gives the example of a doctor who failed to diagnose a cardiac problem with a patient because the patient did not fit the model of a person likely to have a heart attack. The patient complained of all the things a person with angina would complain of, but he was the picture of health. He was in his forties, fit, trim, athletic, worked outdoors, didn't smoke, and had no family history of heart attack, stroke, or diabetes. The doctor wrote off the chest pains the patient complained of as due to overexertion. The next day the patient had a heart attack.

Another example from Groopman illustrates both the representativeness error and the availability error. A patient who appeared to be the model for bulimia, anorexia nervosa, and irritable bowel syndrome was misdiagnosed by some thirty doctors over a period of fifteen years. The more doctors that confirmed the diagnosis, the more available the diagnosis became for the next doctor. But it wasn't until she saw Dr. Myron Falchuk that she found a physician who looked beyond the model that the other doctors had used. Falchuck correctly diagnosed the patient as having celiac disease, an autoimmune disorder (an allergy to gluten) that causes an irritation and distortion in the lining of the bowel, making it nearly impossible for nutrients to be absorbed.

The key to avoiding the representativeness error is to always be open to the possibility that the case before you isn't typical. Force yourself to consider other possibilities. Something may look like a giant airplane flying across the sky, but it may be an illusion caused by having no reference point to correctly estimate the distance between you and the lights you see moving across the sky.

The gambler's fallacy is a type of representativeness error. Because, say, red has come up four times in a row on the roulette wheel, the gambler bets on black because he thinks the odds are against five reds in a row. His model for odds is wrong, however. The ball is as likely to land on red as on black on any given roll (assuming a fair wheel), including on a roll following four reds.

See also anchoring effect and availability error.

further reading

Gilovich, Thomas. 1993. How We Know What Isn't So: The Fallibility of Human Reason in Everyday Life. Free Press.

Gilovich, Thomas. Dale Griffin and Daniel Kahneman. 2002. eds. Heuristics and Biases: The Psychology of Intuitive Judgment. Cambridge University Press.

Groopman, Jerome. M.D. 2007. How Doctors Think. Houghton Mifflin. My review of this book is here.

Kahneman, Daniel. Paul Slovic, and Amos Tversky. eds. 1982. Judgment Under Uncertainty: Heuristics and Biases Cambridge University Press.

Kida, Thomas. 2006. Don't Believe Everything You Think: The 6 Basic Mistakes We Make in Thinking. Prometheus.

Levine, Robert. 2003. The Power of Persuasion - How We're Bought and Sold. John Wiley & Sons.

Sutherland, Stuart. 1992. rev. 2nd ed. Irrationality. Pinter and Martin.

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