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What is a base rate neglect?



 Definition of base rate neglect

Ignoring the base rate refers to a cognitive bias that ignores probabilities and makes judgments contrary to statistics. Ignoring the base rate is also called the base rate error.

Characteristics of base rate neglect

Base rate neglect results in ignoring statistics and making judgments based on impressive subjective experience.

Base rate neglect makes you judge based on your own stereotypes.

Base rate neglect is also related to the representativeness heuristic. Information that comes to mind is given priority over statistics.

Example of base rate neglect

There are people who read the financial newspaper every day and look at the stock market every day.

What kind of job is this person likely to have?

1. This person is most likely a Wall Street brokerage analyst.

2. This person is most likely a student.

The answer is number two. Because of their descriptions of economic newspapers and the stock market, you are likely to think of them as securities analysts. However, the probability is higher for 2.


You don't even need to look at demographics, just look at the probabilities of students vs brokerage analysts for the answer. The number of students is tens of thousands of times greater than the number of analysts at Wall Street securities firms. In other words, the probability that a student will come out is high when one is randomly selected from among those who read economic newspapers every day and who read the stock market every day. No matter how few students read economic newspapers every day and read the stock market every day, even if it is 0.01%, the number is higher than that of analysts at securities firms.

Base rate neglect Three Lines Summary

 -Due to base rate neglect, statistical figures are ignored and phenomena are judged by impressive subjective experiences and stereotypes.

-Base rate neglect is a cognitive bias resulting from quick judgment.
-Mathematical judgment is required to solve the base rate neglect.

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