[pyre]

I think that the line of thought goes something like:

* There's a variance between the number of men and women in field X.

* This gap does not correlate with the number of men and women in the general population.

* Therefore field X must be discouraging women from going into the field that would otherwise be interested in the field.

I believe the thinking is that if everyone did what they wanted to do, then the gender balance in any random field would probably be relatively close to the gender balance of the general populace.