Curious Christian

Survivorship bias is when we only pay attention to the people or things that made it through a situation—and forget about the ones that didn’t. That can seriously mess with our conclusions, because we’re not seeing the whole picture.

The WWII Plane Example

There’s a famous story from World War II that explains this well. The military was looking at returning fighter planes full of bullet holes and trying to decide where to add extra armor. The obvious idea was to reinforce the spots with the most damage.

But a statistician named Abraham Wald had a different take. He said, “Hold on—these planes made it back. That means the bullet holes we’re seeing are in areas that aren’t fatal. What we’re not seeing are the planes that got hit somewhere else and didn’t make it back.” So he recommended adding armor to the areas with fewer bullet holes. Those were likely the weak spots that led to planes being shot down.

The Church Example

Something similar happens when, say, a church wants to understand why people are unhappy or leaving—but they only ask the people who are still attending. That’s a problem, because the folks who stayed might not have experienced the issues that drove others away. So by only listening to current members, the church might completely miss the real reasons people are leaving.

So in both cases, the mistake is focusing only on the “survivors” and ignoring the stories of those who didn’t make it through. To really understand what’s going on, you have to look at who’s missing from the data. This has obvious implications for vetting ministers.