Survivorship Bias

QUOTE

Sherlock Holmes once said…

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.”

CONCEPT

Survivorship Bias

Survivorship Bias is a common logical error that occurs when we concentrate only on the successes and winners of a particular process or event, while ignoring the failures and losers.

This cognitive bias can cause us to draw incorrect conclusions and make poor decisions based on a skewed perspective of reality. It happens because we tend to overestimate the significance of successful outcomes and undervalue the significance of failed outcomes, even if they may provide valuable lessons and insights.

STORY

If It Ain't Broke ... Fix It?

During World War II, aircraft were being shot down at an alarming rate, and the military was desperate to find a solution. They decided to examine the planes that were returning from missions to see where the bullet holes were located.

Based on their analysis, they recommended that more armor be added to the areas that were most heavily damaged.

Abraham Wald, a statistician working for the military, noticed a problem with this approach. By focusing only on the planes that returned, they were ignoring the planes that had been shot down and never made it back. These planes, he reasoned, were the ones that were most vulnerable, and adding armor to the areas that were heavily damaged would do nothing to protect them.

Instead, Wald recommended that armor be added to the areas that were not damaged. This, he theorized, would help protect the planes that were shot in these areas and did not return, and ultimately increase their chances of survival.

The military began implementing his suggestion in their aircraft design. They also started tracking the locations of planes that were shot down and whether they had been outfitted with the new armor.

As it turned out, Wald's theory was correct, and more planes—and pilots—safely returned home as a result.