Survivorship Bias

Day 93 / 365

Why is it that most of us think that music or movies, were better a decade back then they are now? Is the quality really going down with time?

While there might be some truth to that. It’s not the whole story. Part of the reason is that we would only remember the good songs and good movies from the past. The average ones are forgotten. And then, we compare the bad stuff from today from the best stuff we remember from the past, and we conclude — “They don’t make’em like they used to back in my day!”. This is an example of Survivorship Bias.

What’s Survivorship Bias?

Survivorship Bias is a logical error that comes by focusing on a smaller group of people or things while coming to conclusions. It’s a kind of selection bias. The things ignored are often failures, and thus this bias can lead to optimal solutions.

World War II planes

During World War II, the statistician Abraham Wald was given the task to figure out how can the planes be made more immune to bullets. The researchers were analyzing the bullet holes on the planes that came back from battle. Their suggestion was to shield the places which had the most bullet holes.

But Abraham Wald suggested the opposite. He said that the army should reinforce those areas which didn’t have any holes. He pointed out that the study was biased, as they were looking at only the planes that actually survived the missions. They were ignoring the planes that were shot down. The holes in the surviving planes will represent the areas where the plane can take a shot and still come back. The other areas were more vital, as planes hit in those areas were lost completely.

This story is part of my 365 Day Project for 2019. Read about it here

Yesterday’s blog — Why does April fool’s day exist?