[WikiEN-l] Where are the basic demographics on contributors?

[Carl Beckhorn]

I expect that any site with as many active editors as English Wikipedia 
should have good statistical data about members - age, sex, race, 
nationality, and income distributions, among other things. Where can I 
find these statistics for English Wikipedia?  I expect the Foundation 
has at some point retained an independent polling firm to obtain this 
data, right?

 - Carl