Most scientific studies make sense, which is another way of saying that they fit with our everyday experience. Occasionally, though, I bump into a science paper that contradicts something I've long believed in. That's what happened to me when I read about a classic study from the 1980s led by the psychologists Thomas Gilovich and Amos Tversky.
The scientists were interested in how people perceive patterns, and why we so often see patterns that don't actually exist. So far, so obvious: just consider the gambler in Vegas who's convinced that he's found the lucky slot machine. The insight of these scientists, however, was that such delusions weren't confined to casinos or people who didn't know about random number generators. And so they decided to pick an unusual data set: the shots taken by the Philadelphia 76ers basketball team during the 1980-81 season.
What does basketball have to do with false patterns? The scientists noticed that sports fans tended to believe that basketball players were streaky athletes, who went through distinct hot and cold periods. In fact, there was even a name for this phenomenon: "the hot hand." So Tversky and Gilovich decided to conduct a little research experiment. Their question was simple: do players make more shots when they are "hot," or do we just imagine that they make more shots? Is "the hot hand" a real phenomenon?
Tversky and Gilovich began the investigation by sifting through years of 76er statistics. They looked at every single shot taken by every single player, and recorded whether or not that shot had been preceded by a string of hits or misses. (The 76ers were one of the few NBA teams that kept track of the order in which shots were taken.) If "the hot hand" was a real phenomenon, then players should have a higher field goal percentage after making several previous shots. The streak should elevate their game.
So what did the scientists find? There was absolutely no evidence of "the hot hand." A player's chance of making a shot was not affected by whether or not his previous shots had gone in. Each field goal attempt was its own independent event. The short runs experienced by the 76ers were no different than the short runs that naturally emerge from any random process. Taking a jumper was like flipping a coin. The streaks were a figment of our imagination.
The 76ers were shocked by the evidence. Andrew Toney, the 76ers shooting guard, was particularly hard to convince: he was sure that he was a streaky shooter, who went through distinct "hot" and "cold" periods. But the statistics told a different story. During the regular season, Toney made 46 percent of all of his shots. After hitting three shots in a row ? a sure sign that he was now "in the zone" ? Toney's field goal percentage dropped to 34 percent. When Toney thought he was "hot," he was actually freezing cold. And when he thought he was cold, he was just getting warmed up: after missing three shots in a row, Toney made 52 percent of his shots, which was significantly higher than his normal average.
But maybe the 76ers were a statistical outlier. After all, according to a survey conducted by the scientists, 91 percent of serious NBA fans believed in "the hot hand." They just knew that players were streaky. So Tversky and Gilovich decided to analyze another basketball team: the Boston Celtics. This time, they looked at free throw attempts, and not just field goals. Once again, they found absolutely no evidence of hot hands. Larry Bird was just like Andrew Toney: after making several free throws in a row, his free throw percentage actually declined. Bird got complacent, and started missing shots he should have made.
What I find most interesting about this study is that even though I know it's true ? Kobe and Lebron just seem like they're in "the zone" ? I still can't help but believe in the streakiness of NBA players. (After Kobe makes a few shots in a row, I want him to get passed the ball again. And again.) But that belief, like so many of the beliefs generated by the mind, is just a carefully engineered illusion. The world is more random than we can imagine. That's what our mind just can't understand.