Unfortunately, the web cite you reference tells us nothing about how they got
their numbers. I suggest you have a look at the National Center for Education
Statistics (NCES).
The ratio of male to female professors differs by discipline, and some of the
salary difference is explained by the difference in salaries by discipline.
NCES has data on profs by discipline.
There is a 20% difference between Engineering and Humanities profs salaries.
Unfortunately its not broken down by sex.
http://nces.ed.gov/pubs/d96/D96T228.html
Breakdown by sex and rank but not discipline is here
http://nces.ed.gov/pubs/d96/D96T229.html
year and | All |Profes- |Associate|Assistant|Instruc-|Lecturer|
sex | | sor |professor|professor| tor | |
Male | 51,228 | 64,046 | 47,705 | 39,923 | 30,528 | 35,082
Female | 41,369 | 56,555 | 44,626 | 37,352 | 29,072 | 31,677
This contradicts your statements about salary differences across the ranks of
proffesors.
Another point of interest is the age distribution.
Affirmative Action programs geared to rectify imbalences fall strictly on the
young new profs. The old profs are tenured and its difficult to change the
ratios there. NCES also gives the age breakdown of professors.
http://nces.ed.gov/pubs/d96/D96T225.html
Under Age 30, There are as many females as males. For whites the numbers
are identical. For Asians, there are twice as many men as women and for
Blacks there are twice as many women as men. Note that in the general
population there are more men than women in this age group, so equal
representation would have more male than female professors. Apparently, in
this age group males are under represented in faculty positions.