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In Inevitable Illusions: How Mistakes of Reason Rule Our Minds, cognitive scientist Massimo Piattelli-Palmarini explores flaws in the human decision-making process. He focuses on how people deal with probabilities, such as people’s choices when facing various likelihoods of risk and gain.

Overall, I was disappointed with the book. He did a lousy job of dumbing down his presentation to reach a general audience, a difficult task for most experts. He spends a lot of time making the case that people are irrational, which seemed obvious to me when I was a kid hearing Spock say that on Star Trek. A chapter about Bayes’ theorem never writes out that simple equation.

Also, I disagreed with some of his examples. For example,

[A biologist] informs us that both duck eggs and goose eggs contain biotine. How probable is it that a swan egg will also contain biotine?

He argues that you cannot logically justify your intuitive judgment that swan eggs probably contain biotine. However, a basic rule of inductive logic – things that are similar in one respect tend to be similar in other ways – provides ample justification.

Inevitable Illusions presents a few interesting studies that I hadn’t seen before. People in one study were given a fact sheet.

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 antinuclear demonstrations.

They were asked to rank the likelihood of various statements, including these.

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

Most people thought 3 was more likely than 2, even though mathematically 3 implies 2.

Other probability examples, in which people’s choices conflicted with mathematical calculations of how to maximize expected value, were more troublesome. More often than not, my intuition agreed with the calculation, since I wasn’t able to put aside my years of mathematical training. Some of his examples, like the Monty Hall problem, were familiar. Also, since the concept of numerical probabilities only arose a few centuries ago, it’s not clear that wrong answers to probability questions reflect irrationality any more than, say, answering calculus questions incorrectly.

Piattelli-Palmarini views “mistakes of reason” as faults in otherwise rational mind, and better understanding of those mistakes can help us overcome them and act more rationally. My philosophy is rather different: our intuitions, though flawed, are the best guides our limited minds possess when dealing with an intrinsically uncertain world, in which you always have an incomplete understanding of what’s going on and the likelihood of various consequences to your actions.

I’m more impressed with other treatments of the same material, such as the discussion of the psychology of risk in Peter L. Bernstein’s Against the Gods: The Remarkable Story of Risk and Stephen Pinker’s more general book How the Mind Works. Inevitable Illusions may be more appropriate for readers less familiar with probability theory and cognitive science.

posted by Julian at 4:15 PM