Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.

Which of the following two alternatives is more probable?

1. Linda is a bank teller.
2. Linda is a bank teller and active in the feminist movement.

Rationally, statement 2 cannot be more likely than statement 1, but in a 1983 study by Amos Tversky and Daniel Kahneman, fully 85 percent of respondents said that it was.

Why this happens is a matter of some debate. Tversky and Kahneman argued that in making this kind of judgment we seek the closest resemblance between causes and effects (here, between Linda’s personality and her behavior), rather than calculating probability, and that this makes statement 2 seem preferable.