The Linda Problem

Posted on November 29, 2011


I love problems like the one described in this New York Times Article:

Thinking Fast And Slow (it’s a book review and I’ll definitely check the book out)

To see how, consider what Kahneman calls the “best-known and most controversial” of the experiments he and Tversky did together: “the Linda problem.” Participants in the experiment were told about an imaginary young woman named Linda, who is single, outspoken and very bright, and who, as a student, was deeply concerned with issues of discrimination and social justice. The participants were then asked which was more probable: (1) Linda is a bank teller. Or (2) Linda is a bank teller and is active in the feminist movement. The overwhelming response was that (2) was more probable; in other words, that given the background information furnished, “feminist bank teller” was more likely than “bank teller.” This is, of course, a blatant violation of the laws of probability. (Every feminist bank teller is a bank teller; adding a detail can only lower the probability.) Yet even among students in Stanford’s Graduate School of Business, who had extensive training in probability, 85 percent flunked the Linda problem.

This caught me as well.

I don’t think this is about whether people understand probability or not. It’s about the power of patterns on our decision making process and the laziness we exhibit once a pattern is established. I haven’t read the book yet, but I think this is generally their conclusion as well.

I’ve observed this a lot in my experience building websites. If you present something new, say a piece of text, then people won’t bother reading it if it matches a pattern for them. That pattern might be:

  • “This looks like generic salesy text” -> Don’t need to read it
  • “I think I know what this text is going to say” -> Don’t need to read it

Our brain is very good at pattern matching and very lazy, so we look for superficial ways to make decisions based on previous experiences and the patterns we recognize and, barring a difference that is obvious enough to make us question the pattern we’re used to, we won’t put in the necessary effort to figure out whether there is a more subtle change involved or not, leading to confusion or annoyance.

In this case it causes us to get confused and get the problem wrong. We recognize a pattern of two options and make the assumption that option 1 and option 2 are opposite from one another rather than option 2 being a subset of option 1. Even though the text is very explicit, the change is subtle and the pattern is powerful, so we can’t resist using the pattern to bias our decision toward the wrong answer.

If people recognize a pattern that they think lets them take a shortcut then laziness kicks in and they’ll take that shortcut, even if it’s the wrong decision. I guess we’re just good at playing probability games, allowing us to make decisions effectively with less than perfect information.

Personally I think it’s a very powerful force and understanding the phenomenon is important for all sorts of activities, ranging from working in teams, building websites, avoiding fights with your wife, keeping customers happy, reducing the amount of support required for a product etc.

In any case I’ll be checking out this book to see if it provides more of a framework or nuanced information for understanding this idea.