http://www.johndcook.com/blog/2013/02/04/four-hours-of-concentration/
And since this is the Internet, and facts are involved, our gwern turns up there also.
I actually was not talking about myself (self-evaluation is noisy), but people I know.
(self-evaluation is noisy)
Don't tell gwern ...
Although something like "hours worked in a productive manner" should be well quantifiable, for most professions.
http://www.johndcook.com/blog/2013/02/04/four-hours-of-concentration/
And since this is the Internet, and facts are involved, our gwern turns up there also.