UNDERWEIGHTING OF BASE-RATE INFORMATION REFLECTS IMPORTANT
DIFFICULTIES PEOPLE HAVE WITH PROBABILISTIC INFERENCE
Commentary on Koehler on Base-Rate

Abstract

I argue that people do a poor job integrating informative base rates into their decision processes. This is shown by the results of two sorts of study. First, in probabilistic inference word problems, people's interpretations of conditional probabilities are confused. Second, in studies where subjects receive a series of pieces of information and update their probabilities after each, their probability updating is inaccurate, reflecting several error-producing processes, including overweighting of most recent information, which is usually not the base-rate information. We should not ask how much this matters, without considering that experts who make consequential decisions based on their hypotheses about the state of the world usually follow rule-like scripts, rather than explicitly revise probabilities.

Keywords

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