Then-president-elect Obama and his adviser Valerie Jarrett decide on lunch during a stop at Manny's Coffee Shop and Deli in Chicago, Friday, Nov. 21, 2008. (AP Photo/Charles Dharapak)

For the first time in history, a majority of top policy appointments in a presidential administration are held by women and minorities. But if President Obama has put women in so many top posts, why do female White House staffers still earn less on average than men?

To some extent, the answer reflects why there's a gender pay gap in the U.S. workplace more broadly: There are more women in low-level positions.

[Obama has vastly changed the face of the federal bureaucracy]

Women White House staffers still earn 15.8 percent less on average than their male counterparts, according to an analysis from the conservative American Enterprise Institute of the latest disclosure reports. But the 25 highest-earning aides are evenly split -- with 13 men and 12 women each earning between $165,300 and $173,922 a year.

The real discrepancy is at the bottom, where the 100 staffers on the bottom rung -- those earning between $41,000 and $47,631 -- are 57 percent female to 43 percent male.

AEI scholar Mark Perry, who did the study, said that if Obama has managed to make such inroads with his executive branch appointments, “Why can’t he do that at the White House?

Part of it might reflect “the D.C. labor market,” where a disproportionate number of people with 20 to 25 years government experience are men. But he noted that given more women than men are graduating from college right now, there should be a way to level the playing field among White House staff.

Still, women have made gains in the White House over the course of Obama’s administration. While his inner circle of aides was initially mostly male, now half of the department heads in the White House are women.

“Name me a private company where that’s the case,” said a senior administration official who asked not to be identified in order to discuss personnel matters. The official noted that every female assistant to the president besides Valerie Jarrett was promoted from within: Jarrett has held her title from the start of the administration.

“I can’t think of another White House with so many women who have been promoted while the president was in office,” the aide said. “It’s a pretty compelling statistic.”

And when it comes to executive branch appointments, according to University of California law professor Anne Joseph O’Connell, women and people of color face a tougher hurdle than their white male counterparts. They have often taken longer to confirm under this administration, prompting some candidates to withdraw, and others to remain in limbo.

It has taken an average of nearly 117 days for women and minorities to be confirmed since Obama took office, O'Connell found, compared with 86 days for white men. Under George W. Bush, women and minorities were confirmed on average 15 days faster than their white male counterparts.