── ── Cognitive bias

Representativeness Heuristic

The representativeness heuristic is judging probability by how closely something resembles a prototype — overriding actual base rates. Named by Tversky & Kahneman (1972); produces three systematic errors: base rate neglect, the conjunction fallacy (A-and-B feels more likely than A), and insensitivity to sample size.

How it works

Step 1 — Identify judgment + profile: What probability estimate is being made? What profile information is driving it?

Step 2 — Reference class + base rate: What is the base rate of this outcome in the relevant reference class? Was it stated before the profile assessment? (If N while a profile is present, representativeness is active.)

Step 3 — Conjunction test: Does the judgment involve multiple attributes (X and Y and Z)? P(A AND B) ≤ P(A). If the conjunction was rated more probable than a component, the conjunction fallacy is active.

When to use it

• user says 'this person/startup looks like a winner', 'I know one when I see it', 'they have the profile of a great hire', 'this reminds me of [famous success]', or any judgment where a vivid profile drives a probability estimate without an explicit base rate
• Also activate when auditing for the conjunction fallacy or when pattern-matching is cited as the basis for a high-stakes decision

Worked example

Tversky & Kahneman 1972 + 1983 — The Linda Problem

Amos Tversky (1937–1996) and Daniel Kahneman (b. 1934) formed the most productive collaboration in the history of behavioral science. Their program, begun in the late 1960s, systematically documented the ways in which human intuitive probability judgment departs from normative statistical reasoning. Kahneman won the Nobel Prize in Economics in 2002 (Tversky had died in 1996; the prize is not awarded posthumously).