Now I see why the "gender pay gap" myth exists wrote:
Again, maybe you could actually look at the facts, rather than concluding minutely (i.e. in a minute) that it must be "selection bias". Which seems likely the conclusion you want to be true.
I don't know how "critical" your thinking can be when unobserved by actual facts, but then maybe you can make a political pundit as a career.
The OP presented the salary differences observed in the study as the result of some Feminist agenda to inflate the salaries of area studies professors. I simply pointed out that critical thinking would suggest that sample bias in the study is a far more likely explanation than some type of nefarious collusion between colleges and universities to undermine the machinations of the academic labor market. However, fair point that I did not provide any supporting data, so here goes:
According to Google, there are ~2500 4-year, degree granting colleges and universities in the US. Per the OPs link, the salary data was compiled from a survey of 696 4 year, degree granting colleges and universities. The same Google search indicates that there are ~350 bachelors level gender and sexuality studies programs available in the US and only ~75 graduate level gender and sexuality programs. Those sources may be crap, the numbers are corroborated across multiple results. So it's probably a safe bet that only a small minority of US colleges and universities offer a gender or sexuality studies program. So if the studies sample is representative of the composition of US colleges and universities as a whole, then potential for a sample bias is there due to the limited availability of gender and sexuality studies programs. Now you'd just need to confirm that the subset of colleges and universities that have gender or sexuality studies programs have overall higher salary levels than those that do not.
The easiest, quick and dirty way that I can think of to do that is to look at where those colleges are located because salary tends to be highly correlated with cost of living. Here's a map of where universities offering Ethnic, minority, and gender studies degrees are located (hopefully the link works, if not apply the appropriate filter under major):
https://nces.ed.gov/ipeds/CollegeMap/Hmmm. Looks like the coasts, with the highest concentrations in New England, and California. Here's the same map all majors:
https://nces.ed.gov/ipeds/CollegeMap/Far more geographic diversity.
It's no mathematical proof, but seems pretty clear that 1) only a small minority of colleges and universities offer degree programs in gender and sexuality studies, and 2) that minority is dis-proportionally concentrated in high cost of living markets. Infer what you will.