Conjunction fallacy II

And a follow-up on the follow-up. Here is an idea for how to quantify the conjunction fallacy experimentally. Present the subjects with the standard “Linda” story:

Linda is thirty-one 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 antinuclear demonstrations.

But now, instead of asking them to choose the more probable outcome from the two standard options, (1) Linda is a bank teller (2) Linda is a bank teller and is active in the feminist movement, why not ask them to select from a longer list:

  1. Linda is a bank teller.
  2. Linda is a bank teller and is active in the feminist movement.
  3. Linda is a bank teller and is active in the feminist movement and had a lesbian experience in college.
  4. Linda is a bank teller and is active in the feminist movement and had a lesbian experience in college and owns cats.
  5. Linda is a bank teller and is active in the feminist movement and had a lesbian experience in college and owns cats and is overweight.

What is the conjunction size at which the subject begins to realize that increasing the specificity of the outcome is making it less likely?

 

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2 thoughts on “Conjunction fallacy II

  1. What are you trying to measure, the imprecision of language? Get a book of quotations for that.

    I don’t think there’s a widespread “conjunction fallacy:” if your choices are (A) Linda is a bank teller and may or may not be a feminist or (B) Linda is a bank teller and definitely a feminist, you’d get somewhere near 100% answering A. (If not, then that’s actually newsworthy.)

    What might be a real thing is a “correlation fallacy.” Construct some question where the choices are Pr[A,B] more, less, or equal to Pr[A] Pr[B] when the story details give no indication. But even then, people’s priors come into play: if all the women’s college graduates in Philosophy you know are lesbians (my wife notwithstanding), then it’s hardly _irrational_ to use that information in your choice.

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  2. The point of my proposed experiment was to see how long it takes before the subject catches on. We know from experiments that when presented just 1 and 2, many people rank 2 as more probable. What about {1,2,3}, and so on?

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