- Very impressive people.
- Umm... questionable effectiveness in doing what is supposed to be done.
- High status bestowed on these people.
I think this also covers a very high percentage of professional academics (and some other groups), but I'll stick with doctors for a little while.
My impression is that doctors have high status because it's so difficult to become one and because they're doing something good. The puzzle is that their status is very unresponsive to evidence that they're not very effective at doing what it's their job to do, which is improve peoples health. The signal (impressive and good) remains potent. In fact, number crunchers suggesting institutional reform to improve outcomes often get bad press and very negative reactions from doctors (their lower status, I'd guess, because they set themselves up in opposition to people with high status).
I blogged about a similar effect to do with the minimum wage a while back. Supporting the minimum wage is an effective way of signaling that you want to help the poor even if the minimum wage is discredited as a way of actually helping the poor (many economist support the policy despite agreeing that other policies would be better). Arguing against the minimum wage because it hurts the poor is an effective signal that you want to wage class warfare. Claiming that it would be better to top up low wages to whatever level doesn't change the signal.
Loving books is an effective signal about intelligence and learning, but people are loyal to books even when other things become better at doing the things books do.
Giving to charity is a signal of altruism, but many people don't much care how a charity spends the money. Again, the signal remains effective.