The Conjunction Fallacy is another idea that originated with psychologists Daniel Kahneman and Amos Tversky. In 1983 they came up with an experiment known as “The Linda Problem:”

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?

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

Tversky and Kahneman argued that many people would pick the wrong answer here (option 2) because they use a heuristic called ”representativeness.”

To many, the second option seems more “representative” of Linda based on the original description of her: several relatively progressive descriptions, however, there’s no mention of feminism.

Many might assume since she seems progressive, she must also be involved in the feminist movement, even though it’s mathematically less likely that Linda would be both a bank teller and a feminist activist.

However, it’s more probable that Linda is only a bank teller.

This bias directly relates to the UX research team and those who are making decisions based on research insights. Make sure that you are aware of this bias as you synthesize research findings and weigh different options for the team.