Well. As a former Google female employee, I've learned that with 4 years Google experience and 10 years industry experience, I was making as much total comp as a person with about 1.5 years industry experience.
There's a variety of points that would be interesting to compile against. Sex, immigration status, school, company, developer experience, managerial experience, number of startups, number of relocations, average years in any one position, number of children, to think of a few.