Three Things to Consider in Order To Make an Effective Prediction

Michael Mauboussin commenting on Daniel Kahneman:

When asked which was his favorite paper of all-time, Daniel Kahneman pointed to “On the Psychology of Prediction,” which he co-authored with Amos Tversky in 1973. Tversky and Kahneman basically said that there are three things to consider in order to make an effective prediction: the base rate, the individual case, and how to weight the two. In luck-skill language, if luck is dominant you should place most weight on the base rate, and if skill is dominant then you should place most weight on the individual case. And the activities in between get weightings that are a blend.

In fact, there is a concept called the “shrinkage factor” that tells you how much you should revert past outcomes to the mean in order to make a good prediction. A shrinkage factor of 1 means that the next outcome will be the same as the last outcome and indicates all skill, and a factor of 0 means the best guess for the next outcome is the average. Almost everything interesting in life is in between these extremes.

To make this more concrete, consider batting average and on-base percentage, two statistics from baseball. Luck plays a larger role in determining batting average than it does in determining on-base percentage. So if you want to predict a player’s performance (holding skill constant for a moment), you need a shrinkage factor closer to 0 for batting average than for on-base percentage.

I’d like to add one more point that is not analytical but rather psychological. There is a part of the left hemisphere of your brain that is dedicated to sorting out causality. It takes in information and creates a cohesive narrative. It is so good at this function that neuroscientists call it the “interpreter.”

Now no one has a problem with the suggestion that future outcomes combine skill and luck. But once something has occurred, our minds quickly and naturally create a narrative to explain the outcome. Since the interpreter is about finding causality, it doesn’t do a good job of recognizing luck. Once something has occurred, our minds start to believe it was inevitable. This leads to what psychologists call “creeping determinism” – the sense that we knew all along what was going to happen. So while the single most important concept is knowing where you are on the luck-skill continuum, a related point is that your mind will not do a good job of recognizing luck for what it is.

Mauboussin is the author of The Success Equation: Untangling Skill and Luck in Business, Sports, and Investing.