The concept of survivor bias, if you don’t know it, is well worth being aware of. It’s most often used in finance, where it refers to a “tendency for failed companies to be excluded from performance studies” (thanks, Wikipedia). Think of the Dow Jones Industrial Average, which indexes the stock prices of 30 of the largest and most important U.S. companies — until, that is, one of said companies does so poorly that it is booted from the index and is replaced by a company that’s doing better.
Over time, therefore, the DJIA reflects a different reality than many people presume. It is biased toward survivors — or, if you want to think of the concept more broadly, toward winners.
This winner’s bias, if you will, shows up in pretty much every realm imaginable: academics, medicine, politics, etc. I don’t mean to sprinkle skepticism all over your inherently positive thoughts about the world, but I do think it’s worth keeping winner’s bias in mind whenever you read (or write) something about the performance of a given group or institution or coalition.
Winner’s bias is perhaps especially pronounced in sport. The behaviors of winners are remembered and dissected far more thoroughly than those of losers, and given greater weight, even if the outcome was decided by a tiny margin.
In the sports section of yesterday’s USA Today, I came across not one but two subtle examples of this phenomenon, in two articles on the very same page. Both articles discussed the fourth-quarter comeback of a much-favored N.F.L. team in a Monday night game; both contained quotes about a star player urging his team on to success. First, the Patriots came back to beat the Bills:
“When Tom [Brady] came in the huddle at 5:32 and said, ‘Guys, let’s get it going. We’re going to win this game,’ everything just went positive from there,” [Randy] Moss said.
And then the Chargers came back to beat the Raiders:
“L.T. [LaDainian Tomlinson] came over and said, ‘We’re going to win this football game,'” right tackle Jeromey Clary said.
“That kind of got us going again,” [Darren] Sproles said.
I have a simple question: does anyone really think that Brady and Sproles don’t say that kind of the thing in the huddle when their teams are behind and fail to come back?
Attributing causal effect to such a statement might seem natural for a player whose team just earned a big win, or for a sports reporter soaking up the happy locker-room vibe. But if you think about it, this kind of thinking is essentially nothing more than superstition. I’m not saying that people shouldn’t traffic in superstition if it turns them on (yeah, I’ve got a few of my own hoodoos, thanks). But when you’re trying to measure performance, we should remember to not actually believe in it.