Medical Innumeracy in Super Crunchers
By Bryan Caplan
Ian Ayres’ Super Crunchers is full of neat material. But my favorite parts highlight the innumeracy of the medical profession. Most vivid example:
[M]y partner, Jennifer, and I were expecting for the first time – back in 1994. Back then, women were told the probability of Down symdrome based on their age. After sixteen weeks, the mother could have a blood test… and then they’d give you another probability. I remember asking the doctor if they had a way of combining the different probabilities. He told me flat out, “That’s impossible. You just can’t combine probabilities like that.”
Can’t med schools cut one lecture on anatomy to make room for Eliezer’s punchy essay on Bayesian reasoning?
Until they do, of course, you could defend doctors by saying “That isn’t taught in medical school.” So let’s move on to two stories where medical professionals make errors that should embarrass a sixth-grader.
The first involves Ayres’ friend Ben Polak:
“I had a comical interaction with a very nice physician… where she said, ‘One of these probabilities is 1 in 1,000, and one is 1 in 10,000, so what’s the difference?’ and to me there’s actually quite a big difference. There’s a ten times difference.”
The other involves Ayres himself:
I had a similar interaction with a genetic counselor… When I asked for a probability of Down syndrome, the counselor unhelpfully offered: “That would only be a number. In reality, your child will either have it or not.”
In my experience, doctors exacerbate their innumeracy with an idiotic “You can’t be too careful” mantra. It’s almost like something out of a Robin Hanson model.
Actually, it’s exactly like that. Argh.