how many contributors?

[Karl Berry]

Does anyone happen to know of any serious studies on how many
contributors there are in the free software (+ open source) world?

Obviously I'm not hoping for a precise number, since it depends on how
everything is defined (what's a contributor, what's free software/open
source, everywhere in the world vs. by country, etc.).  But I'm guessing
that someone somewhere has probably thought about the question, beyond
"add up all the accounts on savannah, gna, sourceforge, github, ...",
which doesn't seem like a very meaningful number.

Personally, I have participated in a few surveys relating to the topic,
but the results that I have seen are always based on a few hundred or
thousand at most replies.  Not enough to be useful.

As a point of comparison, in the USA, the Bureau of Labor and Statistics
reports about 3.5 million people employed in "Computer and Mathematical
Occupations": http://www.bls.gov/oes/current/oes150000.htm
If I'm reading their info right.  Of course many people employed in other
fields will be FS contributors, and many people employed there are not
contributors, but still, as somewhat solid fact in the river of
speculation, there it is.

Anyway, my web searching hasn't turned up any serious studies, just
anecdotal guesses.  I can make those myself :).  So I just thought I'd
ask.

(I'm not on this list any more, so please cc me on any replies.)

Thanks,
Karl