# base rate fallacy

(redirected from Base-rate neglect)

## base rate fallacy

n
(Statistics) statistics the tendency, when making judgments of the probability with which an event will occur, to ignore the base rate and to concentrate on other information
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(6) The program should include a modest amount of training to deal with typical errors in reasoning, such as overconfidence, bias, and base-rate neglect. (7) The program's participants would make predictive estimates based on numeric probabilities (that is, 40 or 60 percent), rather than possible or probable estimative language.
One mistake, base-rate neglect, is judging probability without taking into account all relevant data.
Kahneman describes dozens of experimentally demonstrated breakdowns, such as anchoring effects, base-rate neglect, availability cascade, illusion of validity, halo effects, framing effects, confirmation bias, availability bias, hindsight bias and others.
We succumb to "base-rate neglect" and fall for sensational stories about school shootings even though they're statistically rare.
We discuss three examples of such research: base-rate neglect, in which people ignore critical background information in favor of less reliable case-specific information; the conjunction fallacy, in which people report that the conjunction of two events is more likely to have occurred than one of the events alone; and the sunk-cost effect, in which people are unwilling to abandon a course of action which has already incurred substantial cost.
In this paper we will briefly review our research in areas (5) through (7) above, namely base-rate neglect, the conjunction fallacy, and the sunk-cost effect.
The literature on base-rate neglect suggests that even when potentially useful information is not aversive we manage to neglect it, instead overemphasizing case-specific information.
Thus, base-rate neglect problems may be thought of as problems involving multiple stimulus control.
But if our students displayed base-rate neglect they should respond even less optimally: They should be sensitive to sample accuracy and match the sample 50% of the time, corresponding to the responses of students in the paper-and-pencil taxicab problem.
In a comparable MTS task pigeons displayed neither base-rate neglect nor even probability matching.
Ongoing research in our laboratory suggests that when pigeons are given a sufficient history of matching and are then tested in our MTS base-rate analog that they too succumb to base-rate neglect. On the other hand, human subjects may be sensitized to the importance of base rates by giving them training in which there is no case-specific information (e.g., no sample), only experience with base rates.
To explain such base-rate neglect, many researchers have invoked a judgment shortcut, or heuristic, known as representativeness, the tendency to assume that like goes with like.
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