A detailed conjunction is judged more probable than one of its own components.
Tversky and Kahneman's Linda problem: told Linda is outspoken and concerned with justice, most respondents rate "bank teller and feminist" more probable than "bank teller." The conjunction cannot be more probable than its component.
In practice
- A risk register entry reading "supplier insolvency during Q3 following the regulatory decision" feels more plausible than "supplier insolvency", and is necessarily less likely.
- A forecast that names the mechanism in detail is believed more and should be believed less.
- Further reading
- Wikipedia
- Subject
- Decision-making & Reasoning
- Essay
- The catalogue of predictable errors