> Some people here (who claim to be intimately involved with the actual financial aspects of running a clinic) say it's the opposite -- that Medicare actually pays the bills so the clinic stays open because the private insurers are so effective at getting out of paying anything.

Oh no, definitely not. Granted, the number I cited is for the aggregate, so it's not going to be exactly true for all practices. Things might look different if you're talking about a public clinic that specializes in low-end care for the poor, but by and large, it's definitely the other way around. Medicare is actually quite notorious among physicians for taking ages to remit payments even for bills that they have approved.

That said, the dynamic usually goes like this:

1. Patient sees doctor for routine procedure
2. Doctor submits bill for $8,000 to private insurer
3. Private insurer says "no, that's way too much, and also you didn't document this part sufficiently"
4. Doctor resubmits bill with more supporting evidence for that part, but a lower total amount
5. Repeat steps 3-4 an arbitrary number of times
6. Insurer says, "okay, to save work next time we'll agree to pay you 400% of what Medicare does for all of these procedures for the next year".

So in that sense, private insurers negotiate their rates, so it seems like they're "getting out" of paying, but in reality they're still paying multiples of what Medicare is.

One confusing quirk: most Medicare patients[0] actually have their insurance plans managed by private insurers, so billing and reimbursements for those would be handled by the private insurers.

> Surely there is a reliable source that can confirm one way or another how this works in practice? I get that it is probably arcane and difficult to understand, but in a country as vast as the US there is probably someone who understands it well enough to summarize for a layman.

The numbers are available in Medicare's annual reports. That's not very user-friendly - last I checked, they were still available in full only on paper(!), and you have to understand financial accounting a little bit in order to parse the numbers yourself. (It's not like they want to make it easy for people to find out how they're under-reimbursing).

Though in terms of secondary sources, if you look at documents written by and for other hospital and insurance adminstrators, you'll find a lot of references to this practice. They don't really talk about it more broadly for political reasons, and also because it's something that's really difficult to explain to the public, and because I'm not convinced the public actually cares.

> but in a country as vast as the US there is probably someone who understands it well enough to summarize for a layman.

There probably is, but getting to my last point - I'm not sure people actually care enough. To be honest, I used to talk about it a lot more on HN (if you search my username + various combinations of "Medicare" or "health insurance", you might find other posts where I've gone into more detail and linked to other materials). But even on HN - let alone with the broader public - I get the sense that most people don't want to understand the complexities of billing and reimbursements and the interchange dynamics between insurers. It makes for a much more complicated narrative than most people are looking for, and so it's easy to gloss over in favor of a simpler one, especially one that fits more neatly into a partisan narrative.

[0] Not most people with Medicare (yet), but most Medicare patients (people with Medicare advantage are a minority, but they account for a disproportionate amount of people who actually use their plans - largely because Medicare is damn-near impossible to use as a patient if you're not on a private network. Ask me how I know that one.)