To put it another way: Even if there was a way to start filling every single open board seat with a woman, according to the Government Accountability Office, it would still take until 2024 to reach parity.

The report, which analyzed data from S&P 1500 companies from 1997 to 2014, found that women now hold roughly 16% of board seats, up from 8% in 1997.

The GAO also dug into which industries have the best—and worst—representation of women on boards. Here’s a look at the top five:

And the bottom five:

The reports turns up some notable differences between female board directors and their male counterparts. Women tend to be younger, with an average age of 60.4, compared to 63.8 for men. Perhaps not surprisingly, female directors also tend to have shorter tenures (42.1% have served for fewer than 5 years, vs. 30.2% of men). They’re also about 2 percentage points less likely to chair a board committee.

Interestingly, women are slightly more likely to serve on more than two boards, with 18.9% of female directors reporting that they sit on three boards, vs. 14.7% of male directors.

The GAO also conducted interviews with 19 “stakeholders” to get a sense of what factors are stopping more women from gaining board seats and to solicit ideas about what might be done to speed up the process. Among the interviewees: Ariel Investments president Mellody Hobson, Macy’s chairman and CEO Terry Lundgren, and BlackRock global head of corporate governance and responsible investment Michelle Edkins.

The group identified a range of factors they say are holding women back, including:

It’s who you know: Directors tend to tap their personal networks to fill open seats. For male directors, that generally means turning to other men.

Tokenism: When one woman is appointed to a board, the emphasis on finding other women peters out. The GAO found that in 2014, 29% of companies in the S&P 500 that had no women on their boards added a woman; 15% of boards with one woman added a second woman; and 6% of companies with two woman on their boards added a third woman.

Low turnover: Since 1998, an average 4% of board seats in the S&P 1500 turn over each year.

What can be done to move things along? The stakeholders had a few ideas:

The Rooney Rule: Require boards to consider a diverse slate of candidates—including at least one woman—for every open seat.

Look beyond CEOs: Because women are underrepresented in CEO roles, boards should also consider women in senior management jobs for a board seat.

Tougher disclosure requirements: While the SEC does currently require companies to disclose whether diversity is a consideration in nominating new members, several of the people interviewed by the GAO said that the requirements are too vague to yield useful information. Indeed, 15 of the 19 stakeholders interviewed support changing SEC rules to require companies to provide more specific diversity information.