Base-Rate Neglect
Base-rate neglect occurs when vivid case-specific evidence overwhelms the background frequency that should anchor judgment.
The Pattern
Base-rate neglect is the failure to give enough weight to how common a condition, event, trait, or outcome is in the relevant reference class. A story about this particular case becomes so vivid that the general frequency quietly disappears.
In Credencing terms, the agent often allows Perceived Evidence to drift away from Objective Evidence because the evidence field has been visually or emotionally compressed. The striking detail is seen; the background distribution is not.
Where the Gap Opens
The main failure is usually Deep Rationality. The Objective Evidence to Perceived Evidence gap (E0-EP) widens because the agent lacks or ignores the statistical frame needed to interpret the evidence. But a Core Rationality failure can appear when the agent knows the base rate matters and avoids it because the anecdote supports a preferred conclusion.
Repair
Repair begins by asking for the reference class. How often does this happen among cases like this? What is the prior probability before the vivid new detail arrives? How diagnostic is the detail relative to the background rate?
The skill is not to dismiss particulars. It is to place particulars inside the right population before allowing confidence to move.
Adjacent References
These are starting points rather than exhaustive citations. They connect this page to nearby work in probability, calibration, cognitive bias, and social epistemology.
- |Daniel Kahneman and Amos Tversky, "Judgment under Uncertainty: Heuristics and Biases" (1974).
- |Sarah Lichtenstein, Baruch Fischhoff, and Lawrence D. Phillips, "Calibration of Probabilities" (1982).