Though headway has been made in bringing women’s wages more in line with men’s in the past several decades, that convergence seems to have stalled in more recent years. To help determine why,  Francine D. Blau and Lawrence M. Kahn, the authors of a new study from the National Bureau of Economic Research parse data on wages and occupations from 1980 to 2010. They find that as more women attended and graduated college and headed into the working world, education and professional experience levels stopped playing a significant role in the the difference between men and women’s wages. Whatever remains of the discrepancy can’t be explained by women not having basic skills and credentials. So what does explain it?

The largest factor in the persistent wage gap is the dearth of women in specific jobs and industries, the researchers found. That means that narrowing the wage gap further requires making high-paying, male-dominated industries like STEM fields and tech companies more enticing and welcoming to women. And even before that, encouraging women and girls to take advantage of opportunities to explore and learn about fields like coding and science that remain male-dominated at both the professional and college level. This could help bring up overall wage averages, though it wouldn’t wholly address the gaps that remain between men and women’s salaries even within high-paying industries.

The study also points to … wait for it … culture, which continues to favor men’s participation in the workforce and women’s participation on the home front. “Current research continues to find evidence of a motherhood penalty for women and of a marriage premium for men,” the report finds. “The greater tendency of men to determine the geographic location of the family continues to be a factor even among highly educated couples.” (The researchers assign minimal importance to theories suggesting that psychological factors such as the notion that men are bigger risk takers, or that women are more averse to tense negotiations have all that much to do with the skill gap.)

“Culture” is kind of a squishy concept. How, precisely, does culture push women’s wages down (or men’s wages up)? They find that one of the more significant contributing factor to pay disparity is due to the fact that women are more likely to spend time away from the workforce and are more likely to work truncated schedules as they try to balance both professional and personal priorities, such as caring for children or parents. Progress in pay parity has been slower among women in highly skilled professions than those in professions that don’t require a college or graduate degree. The paper notes that this may be because women in high-paying, demanding jobs, like doctors or lawyers, are more harshly penalized for time spent away from the office, and clients. Specifically the penalties for time out of the office are high among those with MBAs and JDs.

But it’s also true that these women likely have the option to take more time in the first place. Women with more elite, high-paying jobs typically have better options either via benefits or savings, or family assistance, that can allow them to take time away from the workforce, even if it results in a reduction of overall income.

The researchers note that discrimination, too, can play a role. When it comes to hiring and promotions, concerns that women will (or should) spend more time away from the office, or will somehow underperform can create a labor market where it’s difficult for women to achieve to the most advanced and highly paid positions.