Check the actual base rate before trusting your intuitive estimate
When an event feels common or rare, look up how often it actually happens.
Key takeaways
- What it is: When an event feels common or rare, look up how often it actually happens.
- Why it works: The availability heuristic substitutes ease of retrieval for frequency data. The corrective is to override the proxy with the actual statistic. This works because the base rate is context-free — it does not depend on what you have recently seen or heard — and therefore provides the kind of calibrated prior that availability-biased intuition lacks.
- Evidence: Backed by randomized trials / meta-analyses.
- Avoid: Looking up base rates from sources that are themselves biased toward vivid or unusual events (news media, social feeds) — which re-introduces the availability bias into the "correction."
Why it works
The availability heuristic substitutes ease of retrieval for frequency data. The corrective is to override the proxy with the actual statistic. This works because the base rate is context-free — it does not depend on what you have recently seen or heard — and therefore provides the kind of calibrated prior that availability-biased intuition lacks.
How to do it
- 1Notice when you are making a frequency or probability estimate from intuition.
- 2Ask: "What is the actual base rate for this type of event? Where would I find that number?"
- 3Look up the statistic from a reputable source before finalizing your estimate.
- 4Adjust your intuitive estimate toward the base rate — it rarely needs to move all the way, but it usually needs to move.
What the evidence says
RCT / meta-analysisThe original Tversky & Kahneman (1973) study demonstrated that ease of recall predicted frequency estimates more than actual frequency did. Base rate usage is the standard debiasing recommendation in decision research, supported by the broader reference class forecasting literature.
Honest caveat: Base rate data is not always available, and choosing the right reference class can itself introduce bias. The practice improves calibration but requires a trustworthy source.
- — Tversky & Kahneman (1973), availability: a heuristic for judging frequency and probability, Cognitive Psychology
Common mistake
Looking up base rates from sources that are themselves biased toward vivid or unusual events (news media, social feeds) — which re-introduces the availability bias into the "correction."
IX Coach prompts you to state the base rate for any assumption you’re planning around before accepting your intuitive frequency estimate as accurate.
Practice this with IX Coach →