The base rate fallacy, also called base rate neglect, is the tendency to ignore general statistical information, the base rate, in favor of specific information about an individual case when making a probability judgment. It is often illustrated with the classic disease-screening problem, in which people asked to judge the probability that a person testing positive on a screening test actually has a rare disease tend to overestimate that probability sharply, because they neglect how much more numerous the false positives from the healthy majority are compared with the true positives from the small group that actually has the disease. The fallacy was studied extensively by the psychologists Daniel Kahneman and Amos Tversky as part of their broader research into heuristics and biases in judgment under uncertainty.
Facts
Core ClaimThe fallacy leads people to overweight vivid case-specific evidence, such as a positive test result, while discounting how rare the underlying condition is in the population, which is exactly the reasoning error the courtroom variant, the prosecutor's fallacy, formalizes for evidence such as DNA matches. 1 First Described Year Classification
Type of Phenomenon Connections
Associated With
Studied the base rate fallacy extensively with Daniel Kahneman as part of their heuristics-and-biases research program.
Studied the base rate fallacy extensively with Amos Tversky as part of their heuristics-and-biases research program.
In Branch
Sources
1. Wikipedia: Base rate fallacy
Wikimedia Foundationlead paragraph, definition
The base rate fallacy, also called base rate neglect or base rate bias, is a type of fallacy in which people tend to ignore the base rate (e.g., general prevalence) in favor of the information pertaining only to a specific case.
lead section, defining sentence
The base rate fallacy, also called base rate neglect or base rate bias, is a type of fallacy in which people tend to ignore the base rate (e.g., general prevalence) in favor of the information pertaining only to a specific case.
Findings in psychology section, sentence naming Kahneman and Tversky, cites Kahneman and Tversky 1973 On the psychology of prediction
Psychologists Daniel Kahneman and Amos Tversky attempted to explain this finding in terms of a simple rule or "heuristic" called representativeness.
lead section, phenomenon-kind classification
The base rate fallacy, also called base rate neglect or base rate bias, is a type of fallacy in which people tend to ignore the base rate (e.g., general prevalence).
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