📉Base-rate neglect

Judging how likely something is from how well the case in front of you fits a picture, while ignoring how common that kind of thing is to begin with. The 🔤 Base rate is the prior frequency, and it usually carries most of the information.

In 🔬 Judgment under Uncertainty - Heuristics and Biases people given a short personality sketch guessed a man's profession from the sketch alone. Told how many of each profession were in the group, they still guessed from the sketch. A vivid description beats a dull number almost every time.

Example from work: every launch estimate I have ever given. I looked at the plan, found it convincing and named a date. I never once asked how often a Halden launch arrives on its first date, and I had the answer in my own calendar.

Often confused with: ignoring evidence. It is the opposite fault: too much weight on the specific evidence and none on the background.

Notes: 📖 Tversky and Kahneman on heuristics. What I decided: 💎 A number without its base rate is a story.