There's no citation, but I actually find the part about the hours to be extremely surprising if there are half as many of them doing the same work. Do Germans consume less than half as much medical care? US doctors don't work particularly short hours (even after residency), so it's very surprising if Germans work more considering they usually get much more vacation.
> the AMA has been fixing the supply of doctors
As far as I am aware, the supply of doctors in the US is determined by the number of Medicare-funded residency slots, which is set by Congress.
> No one will argue that we should give up on her.
> What kind of sick society would give up on them?
No one would argue that for your specific examples, but with things like end stage cancer it can be more tricky. Part of the problem is that it is too often framed around "giving up" when it comes to aggressive interventions that are unlikely to help. But doctors who see the system from the inside would generally not choose that path for themselves, for reasons totally unrelated to cost. Too aggressive interventions usually don't make people live longer (they often die sooner!) and can really degrade any remaining quality of life. Atul Gawande wrote a book about it  (interestingly, he's also one of the authors of the paper you cited).
Excessive testing probably isn't purely a defensive medicine thing. I don't have a citation, but apparently when the medical group ordering the tests has a financial interest in the testing center, hugely more testing is done. And of course when the guidelines are unclear it's easier to default to just ordering things, it doesn't cost the doctor anything. There's another article (again by Atul) that touches on it .
It's interesting, if you talk to doctors (in a non-professional setting) they'll generally tell you their profession is getting worse. That they're more and more overworked with no change in pay. And if you look at the statistics, physician pay hasn't gone anywhere while health care costs have skyrocketed. 
 https://www.amazon.com/Being-Mortal-Medicine-What-Matters/dp..., https://www.youtube.com/watch?v=mviU9OeufA0
While Checklist Manifesto is about operational efficiency and quality, Being Mortal is about asking if we're doing the right things in the first place.
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