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Survivorship Bias

The pitfall of studying (only) success
Meera Lee

Imagine a coin-tossing tournament. The last man standing—the ultimate survivor—will have won every single one of his coin tosses in a row. Should we ask him what his secret was?

Don’t laugh; it’s a good bet that at some point in your life you’ve fallen prey to some version of the survivorship bias, an incredibly pervasive cognitive illusion that makes an appearance whenever failures disappear or become hidden from view. Have you ever marveled at the purring engine of a classic car, run your fingers down the smooth seams of a vintage coat, or tested the steel on your grandfather’s old hunting knife? Maybe you thought, “They just don’t make things like they used to!” It’s a romantic idea—that people in some hazy, nostalgic past really valued workmanship and quality; that old objects have a kind of inherent staying power.

What you probably didn’t think about, in those moments, were all the classic cars that ended up broken down in junkyards. You didn’t consider the coats whose seams had already fallen apart. All you saw were the things that survived to tell their stories. In the context of antique shopping, its effects are fairly innocuous—but David McRaney offers an intuitive example of survivorship bias and a matter of life and death at his blog You Are Not So Smart. During World War II, McRaney explains, military engineers wanted to figure out how to make bomber planes safer for the pilots who risked their lives to fly them. When the engineers looked at returned planes, they saw that bullet damage clustered in three main places: the wings, the body, and the rear gunner. These, then were the places they suggested be reinforced with extra armor.

Fortunately for the army, it had the help of a statistician named Abraham Wald. These planes, Wald pointed out, had survived being hit. What they showed was that a plane could get shot multiple times in the wings, body, and rear gunner and still manage to fly. It was the rest of the plane that needed reinforcement.

Once you’re attuned to the way survivorship bias works, it’s hard not to see it rearing its head all over the place. You might realize that the friends who urge you to take up knitting (“It’s really easy!”) so you can have fun and save money while outfitting your entire family in cute hats and sweaters don’t include the ones who’ve thrown away their needles in a disastrous tangle of wool. You might suss out the reason your new date has nothing but fruit and vegetables in the fridge: He’s already eaten all the junk food.

And you might understand why looking at the life stories of successful people won’t necessarily do you any good. Is it true that Bill Gates and Maya Angelou both dropped out of college? Well, yes—but given that over a third of each enrolled class of students in the U.S. drops out before graduating, and there are only a handful of Microsoft founders and poet laureates, this hardly seems like a defining characteristic. To really understand the secret of success, we would have to look at examples of lots of college dropouts—including the ones who failed.

From the Being Human perspective, survivorship bias represents yet another way our brains manufacture a skewed model of the world, which we then unquestionably take for reality. The important thing about survivorship bias is that if we aren’t wary, it can create secrets of success where none exist. After all, we won’t always know we’re looking at a coin-toss.
 

naveen k
2 years ago

Human guys, says de Waal, appear to have gotten to be uncomfortable with participating in obvious strategic maneuvers. Yet on the most fundamental level, they're the same as their primate relatives. Take the way Bob Woodward and Carl Bernstein depict Richard Nixon's post-Watergate wails and yells in their book The Final Days, he composes. There is a route in which Nixon's despondency can be seen as rather primal. 

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