Polygenic Risk Scores Might Be Bullshit

A reminder that accuracy in a group does not equal accuracy for an individual.

I was really struggling to think of a good analogy to explain the glaring problem of polygenic risk scores this week. But I think I have it now. Go with me on this.

An alien spaceship parks itself, Independence Day style, above a local office building.

But unlike the aliens that gave such a hard time to Will Smith and Brent Spiner — these are benevolent, technologically superior guys. They shine a mysterious green light down on the building and then announce, maybe via telepathy, that 6% of the people in that building will have a heart attack in the next year.

They move on to the next building. “Five percent will have a heart attack in the next year”. And the next — 7%. And the next — 2%.

Let’s assume the aliens are entirely accurate. What do you do with this information?

Most of us would suggest you find out who was in the buildings with the higher percentages. You check their cholesterol, get them to exercise more, do some stress tests, and so on.

But that said, you’d still be spending a lot of money on a bunch of people who were NOT going to have heart attacks. So, a crack team of spies — in my mind this is definitely led by a grizzled Ian McShane — infiltrate the alien ship, steal this predictive ray gun, and start pointing it — not at buildings — but at people.

This person has a 10% chance of having a heart attack in the next year. This person has a 50% chance. The aliens, seeing this, leave us one final message before flying into the great beyond: “no, you guys are doing it wrong”.