Tuesday, February 16, 2010

When Extra Information Makes Us Dumber

Eric is 57 years old, very intelligent, opinionated, and empathetic. He is interested in politics. He has a beard, glasses and is generally friendly. He plays guitar in a band with some of his other mid-50s friends. The band periodically performs at venues in a nearby city.

Rank the following statements about Eric : (1) is "most likely to be true" to (7) least likely to be true.

Eric is a(n):

  • Member of the top 20% of his college class
  • Car salesman who has been involved in anti-war protests
  • Daily reader of the New York Times
  • Ex-high school track and field runner and never went to college
  • Car salesman
  • Bachelor
  • Daily reader of the Wall Street Journal
Write your answers down.

Now look at two of the responses on the list: "Car salesman who was has been involved in anti-war protests" and "Car salesman." Which one did you rank as more likely?

If you picked "Car salesman who has been involved in anti-war protests," think again. You are logically incorrect. It is impossible that being both a car salesman and an anti-war protester is more likely than just being a car salesman.

However, we really want Eric to be an anti-war protester - a bearded, glasses-wearing, guitar-playing protester. The description just seems to fit! In fact, it fits so well that the information about "anti-war protests" trumps the information about being a car salesman. The extra information that I gave about Eric is both superfluous and misleading.

Next time you make an important decision, take another look. Are you using more information than you need to in your decision process? More importantly, is it misleading you?