Currently, all OECD countries other than the United States have some kind of national paid parental leave policy. The most generous policies are found in Europe, where the length of paid maternity leave can be as long as 3 years, with up to 100% wages covered. Two-thirds of developed countries provide some limited rights for fathers to take family leave, as well.

In the United States, the 1993 Family and Medical Leave Act (FMLA) requires that employers provide 12 weeks of family leave to qualifying workers with a newborn or a sick child, spouse, or parent, but that leave is unpaid. California was the first of three states to introduce a paid family leave program in 2004 (the other states are New Jersey in 2008 and Rhode Island in 2014). California Paid Family Leave Statute (CA-PFL) offers six weeks of paid leave to new parents, with almost universal eligibility among private sector workers.

Numerous studies have been done on maternity leave and child care in relation to women's labor participation: Evidence strongly suggests that women increase their leave-taking when paid family leave is available. However, we know very little about how fathers respond to paid leave. Fathers may not take time off even when it's available due to cost, since men usually earn more than women (currently, CA-PFL provides 55% percent wage replacement, up to a ceiling of $1,104 per week in 2015). Men may also decide against taking parental leave because they perceive stigma, fearing that coworkers or employers may consider them less committed to their work, which may jeopardize future promotions or even current employment.

New research on the effects of paid paternity leave may help us understand how family-friendly policies affect the amount of time fathers spend on childcare, not only during the period of leave, but throughout a child's life. We do know that currently, fathers tend to take very little time off work compared to mothers. The study found that "14 percent of employed mothers of children under age one reported being on leave versus less than two percent of employed fathers, and these rates have remained very stable over the past decade."

If so few men take parental leave, who are the 2% who do?

According to the study led by Maya Rossin-Slater at the University of California at Santa Barbara, there are three categories of fathers who take paternity leave under California's first-in-the-nation gender-neutral paid family leave program.

Father who have baby boys are much more likely to take paternity leave than fathers who have baby girls. "The overall effect of CA-PFL on fathers' leave-taking is about twice as large for fathers of sons than for fathers of daughters," according to the study, which used data from the 2000 Census and the 2000-2013 waves of the American Community Survey (ACS) to identify the causal effects of paid family leave on paternal leave-taking.

If we were to consider only fathers married to employed mothers (who are eligible for a longer period of family leave as the primary parent), we see that fathers of boys are even more likely to take parental leave. In fact, fathers of girls do not take a longer period of parental leave even when paid family leave is available. Fathers were also more likely to take sole parental leave if they had sons--but not if they had daughters.

Why do men take more paternity leave for sons? See part 2 of this series for some explanations.