Something came up in another post that I think can be settled by reference to actual published studies:
How many hours should a TYPICAL software developer work over the LONG TERM in order to maximize his/her TOTAL productivity?
Note that I'm talking about a software developer doing software development work. I seem to remember a Steve McConnell book where he actually gives a figure from published studies, but I'll have to go look it up. And I'm sure there are others. I'm hoping by "crowdsourcing" this question I get a more complete answer.
Note that I'm not talking about the number of hours over which you maximize your average productivity - that isn't my question. I'm talking about the point at which, if you do more hours of work long-term, you will actually reduce your total productive output due to making mistakes. Note that this is not an opinion-based question either - I'm hoping I can find stuff from actual scientific studies.