For many years, the United States outperformed most of the developed world in women's  workforce participation. Indeed, in 1990, only five countries  -- Norway, Denmark, Sweden, Finland and Canada -- had higher labor force participation rates among women. The United States bested Germany, France and Japan, among many others. But as of 2010, that's changed:

Not every other country has made progress. Japan has remained steady, with about the same low rate of women's workforce participation as it had 1990, and Sweden lost some ground, though its number is still quite high. But on average, other countries have improved at a quicker rate than America. Spain and Italy, in particular, had massive 31.4-point and 17.7-point jumps, and Germany and France also saw double-digit increases in the rate of women's participation in their workforces. The United States, however, gained only 1.2 points over the 20-year period.

What's the explanation? A new working paper from Francine Blau and Lawrence Kahn, two professors at Cornell University's labor school, considers how and why the United States lost so much ground. A major factor, the researchers found, is the divergence between the U.S. and other countries' family leave and other work-life policies, a gap seen back in 1990 that has since widened considerably.

Yes, we're still talking about "women in the workforce" as though that's an  unusual thing for "girls." Working women Melanie Griffith and Sigourney Weaver fought for respect in 1988's  "Working Girl." (20th Century Fox)

In 1990, the United States offered no mandated parental leave time, compared with a non-U.S. average of 37.2 weeks. By 2010, the United States was offering 12 weeks' leave, but the non-U.S. average had leaped to 57.3 weeks. Neither in 1990 nor today did the United States provide public paid leave, while other countries paid, on average, 26.5 percent of previous wages in 1990 and 38 percent today. Blau and Kahn found that about 28 percent to 29 percent of the decline in the American female labor force participation can be explained by the relative stinginess of its family leave and part-time work policies.

But the United States doesn't falter in every work-life area. Blau and Kahn found that much of the participation difference between the United States and other countries is attributable to higher rates of part-time work in Europe relative to the United States. Their numbers showed that 13.1 percent of American women work part-time, compared with a non-U.S. average of 26 percent. And while the incidence of part-time work is falling in America, it's rising slightly abroad. Overall, Blau and Kahn found, 55 percent to 65 percent of the job gains prompted by more generous family leave policies are in part-time work. Given that part-time workers are often paid less and have fewer benefits than full-time labor, that's a significant caveat.

American women are also far more successful than their foreign counterparts in attaining positions of authority in companies. Men and women are equally likely to be managers in the United States, the researchers found, but women are half as likely to fill that role in other countries. In all countries, women are more likely than men to hold "professional" positions as doctors, lawyer, and so forth, but the gap is wider in the United States than elsewhere.

So, the authors conclude, there's a trade-off. Generous leave policies promote women's continued participation in the labor force, but they also are associated with gender inequity within organizations.