Love & Money is a MarketWatch series looking at how our relationship with money impacts our relationships with significant others, friends and family. This story was republished for International Women’s Day on March 8.

On Equal Pay Day, the glass ceiling remains “firmly intact” even among the uber-wealthy.

That’s according to recent research published in the peer-reviewed American Sociological Review. A household’s 1% status — a threshold calculated here as nearly $845,000 in 2016 dollars — is “rarely obtained” through women’s income, it found. Women’s income alone qualifies them for 1% status in just 5% of elite households, while women’s income is “necessary” to nudge a household over that threshold in just 15% of households.

“ The 10 richest people in America are all men, according to Forbes’ annual list of the 400 wealthiest Americans. ”

“Although self-employment and higher education increase the likelihood that women will personally earn sufficient income for 1% status, marrying a man with good income prospects is still a woman’s primary route to the 1% due to labor-market inequalities,” study co-author Jill Yavorsky, an assistant professor at the University of North Carolina at Charlotte, told MarketWatch.

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An even bleaker finding: This gender gap has persisted for decades. “Women have made virtually no progress in earning enough income to qualify for top-1% status since the mid- to late 1990s,” Yavorsky said.

The researchers used 1995 to 2016 data from the Federal Reserve Board’s Survey of Consumer Finances. Their findings, Yavorsky said, point to “a persistent male dominance of income resources in top-1% families.” While that doesn’t mean women in top-1% households are “disempowered or marginalized,” she and her co-authors added, it does suggest that they don’t wield as much “substantive” power as their male counterparts.

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If women’s income proves relatively trivial in most elite households, then a major driver of income inequality is “a small group of men’s income disproportionately rising compared with all others,” wrote Yavorsky and her co-authors Lisa Keister of Duke University, Yue Qian of the University of British Columbia and Michael Naud of the Ohio State University. (Consider, for example, that America’s top 1% made 26.3 times as much as the other 99% in 2015.)

The 10 richest people in America are all men, according to Forbes’ annual list of the 400 wealthiest Americans published in October.

“ Women qualify for 1% status in just 5% of elite households, while women’s income is necessary to reach that threshold in just 15% of households. ”

The first woman on the list, Walmart WMT, +0.90% heiress Alice Walton, clocks in at No. 12 with a $44.9 billion net worth — trailed by Mars candy heiress Jacqueline Mars at No. 18 ($24 billion), philanthropist Laurene Powell Jobs at No. 20 ($20.5 billion), widow of the late Apple AAPL, +1.57% CEO Steve Jobs, and Fidelity Investments FNF, +1.62% CEO Abigail Johnson at No. 28 ($17.3 billion).

MacKenzie Bezos, the estranged wife of world’s-richest-man Jeff Bezos, founder and CEO of Amazon AMZN, +5.69% ), is poised to become the world’s richest woman should she exit their divorce proceedings with half of their $139 billion fortune ($69.5 billion).

Inequalities within the home also keep women behind, Yavorsky suggested. Mothers are more likely than fathers to undergo career interruptions like reduced work hours, taking a significant amount of time off or quitting a job, according to a 2013 Pew Research Center report.

What’s more, women spend more time on child care and housework than men do, Yavorsky pointed out, “in ways that can hurt their future earnings.” Yavorsky laid out three ways to help boost women’s likelihood of landing top-income positions:

• Provide greater access to financial capital to help women entrepreneurs start and grow their business.

• Change hostile or biased cultures within male-dominated elite fields — like finance and law — “that prevent women from entering them in the first place, or push them out once they do enter them.”

• Promote women to more high-level leadership positions.

Yavorsky and her colleagues’ findings, she said, signify “a broader labor-market inequality issue between men and women” in which men’s human capital — like education and entrepreneurship — works far more efficiently in gaining them top income.