Huh

My Dad has always been suspicious of dentists overservicing, giving you lots of treatments you didn't actually need. While this didn't seem implausible, I wasn't entirely sold on the (highly ad hoc) way he seemed to arrive at this conclusion.

As evidence on the subject, check out this gem from Dan Ariely, in an interview with NPR:

Professor DAN ARIELY (Behavioral Economist, Duke University): So, you know, you go to a dentist and the dentist - X-ray your teeth, and they try to find cavities. And one of the - question you can ask is, how good are dentists at that, right?

Prof. ARIELY: So imagine: You came to a dentist; you got your X-ray. And then we took your X-ray, and we also gave it to another dentist.

Prof. ARIELY: And we asked both dentists to find cavities. And the question is, what would be the match? How many cavities will they find, both people would find in the same teeth?

SIEGEL: And I'd really hope it would be somewhere up around 95-plus percent.

Prof. ARIELY: That's right. It turns out what Delta Dental tells us is that the probability of this happening is about 50 percent.

SIEGEL: Fifty percent?

Prof. ARIELY: Fifty percent, right. It's really, really low. It's amazingly low. Now, these are not cavities that the dentist finds by poking in and kind of actually measuring one. It's from X-rays. Now, why is it so low? It's not that one dentist find cavities and one doesn't. They both find cavities, just find them in different teeth.

(Soundbite of laughter)

Prof. ARIELY: And here is what happens. Imagine you're a dentist, and you see a patient, and you really want to find a cavity because you get paid more if you find cavities and you can fix them. And the patient is already on the chair. He's already prepped. You might give them the treatment right now, really good marginal income for you. How is this motivation to find cavities - will influence your ability?

Now, you look at an X-ray - which is a little fuzzy and unclear, and there are shadows and all kinds of things are happening. What happens is this unclarity of the X-ray helps, in some sense, the dentist to interpret noise as signals, and find cavities where there aren't really any.

SIEGEL: And fill them?

Prof. ARIELY: And fill them, and drill them, expand them. I don't think they ever tell their patients, hey, I thought it was a cavity but turns out it was just a mistake.

If I had more time and less money, I'd definitely consider taking my x-rays to multiple dentists and only filling the teeth that multiple dentists agreed on. As I don't, I end up following the procedure used in so many cases of big information asymmetries: bend over and take it.