But add in controls for differences such as age, education, years of experience, industry, job titles and location, and the gap shrinks considerably, to just 5.4 percent, Glassdoor found. This is the "adjusted" gap, or the part of the difference for which Glassdoor can find no obvious explanation other than potential differences in how men and women negotiate, simple bias on the part of employers or other unexplained differences.
Glassdoor's chief economist, Andrew Chamberlain, said that even if that 5 percent unexplained gap may seem small to some, he was surprised by it. "Before I started this paper five or six months ago, I thought once we controlled for job titles and companies, there was going to be almost no gender pay gap involved," he said in an interview. "There’s a risk that in this paper showing a 5 percent pay gap, many people might think that’s minimizing the problem. But I'm actually surprised it’s not smaller than 5 percent. That's pretty significant, and a pretty decent chunk of change over a lifetime."
Meanwhile, for some occupations, Glassdoor found that "adjusted" gap to be much higher than 5 percent. For computer programmers, chefs and dentists, it's 28 percent. For psychologists and C-level corporate executives, it's 27 percent. Even among retail representatives and medical technicians, the gap is nearly three times what it is for the broad population, Glassdoor found.
Their analysis, it should be noted, comes with some caveats. For one, its sample comes from self-reported data by people who are Internet users aware of Glassdoor's site, so does not claim to reflect the overall job market.
In addition, some of the sample sizes are relatively small -- there were 138 people in its sample of computer programmers, and just 61 dentists. (Other fields, such as computer-aided design, were significantly higher, with 1,044 salary reports, and nearly 11,000 for retail representatives.) Chamberlain notes that one possible explanation for why the gap is high among computer programmers is that it's an older field focused on mainframe computers and therefore is still populated by more men. "If you have a heavily male-dominated field, these are the people who are in managerial roles, and they're the ones making pay and promotion decisions," he says.
There also may be wide variation within job categories. For instance, it finds a gender pay gap of 18 percent for physicians. But it doesn't break out the different specialties that would fall into that category, such as a comparison of relatively lower paid pediatricians with much more highly paid orthopedic surgeons, where pay and gender makeup vary widely.
Still, until more data is available at a more granular level, Glassdoor's research offers a striking snapshot of where the biggest gap is: At the top of the pay scale, generally. According to Glassdoor's analysis, several of the occupations with the widest gender wage gap are also among the highest paid -- jobs like C-suite executives and physicians. "It turns out a lot of the ones on the high end are very male-dominated fields, and the ones on the low end are very female-dominated fields," Chamberlain says.
The study comes on the heels of a recent report about research showing that when women enter male-dominated fields, pay appears to decline. The New York Times reported on the study Friday, which examined U.S. Census Bureau data from 1950 to 2000 and found that when women started working in large numbers in traditionally male fields, those jobs began paying less, even after controlling for factors that could skew the results, such as experience, education and geography.
Glassdoor's study did find a few job categories where women out-earn men, including social workers, merchandisers, research assistants and purchasing specialists. And the job that comes closest to absolute gender parity, according to Glassdoor? It's event coordinators, where women report making just 0.2 percent less than men.
As the gender pay gap increasingly draws attention and comes under regulatory scrutiny -- California's new Fair Pay Act requires employers to be able to prove they pay equitably for similar work, and President Obama proposed new rules in January requiring companies to report pay data based on race, gender and ethnicity -- Glassdoor says more employers are wanting to promote their practices.
Dawn Lyon, the site's vice president of corporate affairs, said in an interview that many employers have begun listing a pledge to maintain equitable pay practices on their benefits page on Glassdoor's site since the feature was rolled out last spring. "I think we will see more employers using it to differentiate themselves in the marketplace," she said. "But that doesn't mean it doesn't come without work and effort."
If Glassdoor's analysis is right, managers in some job categories will have more work than others.