Smart Thinking

Fooled by the Conjunction Fallacy

The Conjunction Fallacy – getting fooled by Representativeness and how to avoid its logical mousetrap.

Understanding the Conjunction Fallacy…

Conjunction Fallacy

A frequently cited example of this fallacy comes from Amos Tversky and Daniel Kahneman:

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.

85% of those asked chose option 2, whereas the probability of two events occurring together (in “conjunction”) is always less than or equal to the probability of either one occurring alone.

Logically Fallacious: The Ultimate Collection of Over 300 Logical Fallacies

Representativeness Heuristic

This seems to occur because of the Representativeness Heuristic, in each case the more detailed second statement seems more representative of the person described in the back-story.

This goes beyond being an interesting anecdote. In Pattern Based Strategy, pattern detection and analysis (as well as hypotheses and probabilities of occurrence) need to be taken into account. To get ‘fooled by the back-story’ and the basics of probability (i.e. unless we know with absolute certainty that Linda is an active feminist), then statement 2 must be less probable.

Fooled by Representativeness

Nassim Taleb introduced us to Fooled by Randomness. There is also merit in not being fooled by detail, Representativeness and incorrect understanding of probability. Pattern seeking could be skewed by Conjunction Fallacies and specious hypotheses.

Fooled by Randomness: The Hidden Role of Chance in Life and in the Markets

Further Reading on Nassim Nicholas Taleb

By Steve Nimmons

Steve is a Certified European Engineer, Chartered Engineer, Chartered Fellow of the British Computer Society, Fellow of the Institution of Engineering and Technology, Royal Society of Arts, Linnean Society and Society of Antiquaries of Scotland. He is an Electric Circle Patron of the Royal Institution of Great Britain, a Liveryman and Freeman of London and serves on numerous industry panels. He is a member of Chatham House, the Royal United Services Institute and the Chartered Institute of Journalists.

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