Conjunction fallacy

We think that specific conditions are more probable than a single general condition.

Example

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 is more probable?

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

More people pick option two - even though its a subset of option 1.

Cause

• People use representation heuristic to calculate the probability - option 2 seems more "representative" of Linda
• Framing Effect