What is Survivor Bias?
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Ok, so let’s pretend that you’re a WWII aeroplane designer. Your job is to make sure planes return with their pilots in tact. This means you gotta find out where to put armour.
In an ideal world, you could armour the whole plane. Problem is, both fuel & metal are expensive, so you only wanna put armour where it’s needed.
So, you make a rule. “Whenever a plane gets back to base, a group of people will check it top to bottom for bullet holes, and record where they are.
You wait about 5 months, then look at the data. Most bullet holes are found along the body of the planes. The only places where bullets are absent, are the cockpit, the engines, the rudders, and thin parts of the tail.
Where do you put armour?
A novice would recommend that you put armour where the bullet holes are, because that’s obviously where planes are getting shot. But this is flawed.
Think about it: What happens when a plane gets shot in the engine? It crashes. What if it’s shot in the cockpit? Well, the pilot dies, so it crashes. Rudders? Plane can’t keep steady, so it crashes.
Whenever a plan is shot in those places, that plane never gets back to base. That means your men never find a plane that’s damaged there, and you never hear about it.
That is the survivorship bias in play.
Sometimes, the way you gather information will skew the results you get. You have to account for this in order to give an accurate assessment..
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