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Note Book

Winter 2006 • Volume 12, Issue 1

Which psychological processes involved in
decision making are most interesting to you?

Weiten I Griggs I Stalling

Dr. Richard Griggs ’70
University of Florida

Griggs imageI am most interested in the judgment heuristics (general rules of thumb) that people use in making decisions, especially about the likelihood of events. We use these heuristics because they usually lead to reasonably good, speedy judgments; however, the downside is that they sometimes lead to very predictable errors. To understand how, we’ll consider two well-known heuristics and some simple problems that illustrate their use. To get started, read the following personality sketch and then answer the question that follows

Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was concerned with issues of discrimination and social justice, and also participated in antinuclear demonstrations.
Which of the following is more likely? Linda is a bank teller, or Linda is a bank teller and active in the feminist movement.

If you are like most people, you decided that the second alternative is more probable. Not so! There are clearly more bank tellers than feminist bank tellers. The conjunction of two different events (bank teller and feminist) cannot be more likely than either event alone (in this case, bank teller). We ignore this simple probability truism. So how do we make such decisions? We use the representativeness heuristic—judging the likelihood of category membership by how well something matches a particular category (the more representative, the more probable). Linda matches your idea of a feminist more than a bank teller and, via the heuristic, you incorrectly judge the probability of the conjunctive event to be greater.

Try another one. Does the letter r occur more often as the first letter or the third letter in English words? People most often say in the first letter position. Why? Using a heuristic leads us astray again. We are using the availability heuristic—judging liklihood by availability in memory (the more available, the more probable). Because it is much easier to think of words that begin with a letter than have the letter in the third position, we decide that they are more probable. However, this is not the case for r or k, l, n, v, x, and z.

Now consider the following finding. Many people think that seven-letter words ending in ”ing“ are more frequent than words with ”i“ as the fifth letter. Why? Availability strikes again. Seven-letter words ending in ”ing“ (e.g., resting) are easier to imagine, but note that every one also has ”i“ in the fifth position as do many other words not ending in ”ing“ (e.g., reality). Thus, counter to the heuristic, they are not more probable. This should also help you to understand the answer to the Linda problem. Just as there are some seven-letter words with ”i“ in the fifth position that do not end in ”ing,“ there are some bank tellers who are not feminists.

To learn more about these heuristics and human decision making, I strongly recommend Scott Plous’s engaging book, The Psychology of Judgment and Decision Making.

 

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