Even when you control for factors like race, education, profession, location, and even number of children, lesbians still make about 6% more than straight gals. There are a lot of theories about why this happens (I, for one, am curious as to whether lesbians are more likely to negotiate for raises than straight women), but one theory centers around the idea that straight women expect to, eventually, be involved with a man. And they expect, just as reasonably, that that man will earn more than they do—and, thus, when it comes time to decide who will make career sacrifices, the women expect that they'll be the ones to take that hit. All those assumptions make sense—given what we know about American life—and they all lead to straight women investing less human capital in their careers. Anyway, that's the theory tested by a 2009 study explained by The Big Think blog:
This theory is cleverly tested in a paper which calculates the wage premium paid to lesbians in two distinct groups--those who were once in a heterosexual marriage and those have never been married.* The assumption made is reasonable; lesbian women who were once married to men (about 44% of the lesbians in the sample) presumably have in the past had the expectation that they would have a marriage partner with a higher income. The never-married women might also have had this expectation, but it is much more likely that, on average, women in that group expected to be in a relationship with another woman with a comparable income.
Does the evidence support the theory that the wage premium can be explained by greater investment in more market-oriented skills by lesbian women? Well the premium does not disappear completely for the subset of previously married women but is reduced by about 17%, providing some support for the idea. At 5.2% though, the once-married lesbian premium is still high enough that I don't think we can consider the case closed.
So why does the lesbian wage premium exist? Nobody is really sure. Hopefully further research will make more sense of this. I'm posting about it mainly because I had no idea this phenomenon existed, until I read the Big Think story. Some other research angles I'd love to know more about: Whether some lesbians make more than others and whether that can be correlated to differences in social circles and personality; what do high-earning straight women and high-earning lesbian women have in common; and (from a more navel-gazing perspective) where do bisexual women stand?