Another year, another Time Use survey from the Department of Labor - and another eyebrow-raising revelation that men log more hours at work than women.

Those who argue both genders receive equal pay for equal work, once you control for choice, often point to the annual report , which breaks down how Americans pass their days.

Since 2003, when government researchers started collecting the data, men have reported devoting more life to paid labor than their female counterparts. In 2015, employed men recorded working an average 42 minutes per day longer than employed women. Women, meanwhile, said they spent more time on housework: 2.6 hours, compared to the men's 2.1 hours.

"This difference partly reflects women's greater likelihood of working part time," the authors explained.

"However, even among full-time workers (those usually working 35 hours or more per week), men worked longer than women-8.2 hours compared with 7.8 hours."

Maybe that's why the average wages for a working woman in the United States comes out to be 79 cents for every dollar paid to the typical working man, some say. Writes Charlotte Hays for the Independent Women's Forum, a right-leaning think tank in the nation's capital:

"We definitely are against pay discrimination on the basis of gender, but it still should be observed that this data runs counter to the equal pay for equal work movement: This data shows that women and men take different roles in the workplace - and these choices should be factored into any claims about a gender wage gap."

She's not wrong. But nothing about the gender wage gap is simple, as much as experts on both sides of the ideological aisle would like it to be. Economists say the controversial figure isn't a product of pure job decision or discrimination; it's likely a blend of both, plus a dose of societal conditioning and pressure.

Let's start with a few massive caveats in the Labor Department's report. First, the researchers asked each respondent to log their own time. Nobody submitted manager-approved work hours, and research tells us one of sexes generally tends to overestimate. Secondly, the survey didn't measure productivity or efficiency. Workaholism isn't necessarily a sign of value.

Onto the anatomy of the female paycheck: Cornell University researchers Francine Kahn and Lawrence Blau, who've looked at the wage gap for years, found in a 2015 study that chunks of the gender wage gap can be attributed to industry choice (17.6 percent) and occupation choice (32.9 percent). We know that women often concentrate in lower-paying roles, while men gravitate toward higher-paying fields, such as technology and finance. (Whether those realms are hostile toward women remains a topic of hot debate.)

Another 38 percent of the gap, however, remains unexplained.

Blau and Kahn chalk this up to potential discrimination, conscious or not. Perhaps an employer is inclined to pick a man over an equally qualified woman for a promotion, assuming he'd work harder. Perhaps a woman loses out on a prestigious role because a manager fears she may soon get pregnant . Perhaps she's perceived as too severe when a male applicant appears confident.

In one 2005 study , Carnegie Mellon economist Linda Babcock showed people clips of men and women asking for a raise, following the same script. Male viewers deemed the men's negotiating style smooth, while women using identical words registered as too demanding.

Women aren't born with an innate desire to, say, do the dishes while her partner works - just as men don't come into this world with the instinct to work 50 hours each week as a banker while his partner bonds with the kids. But unpaid labor has long disproportionately fallen on women's shoulders.

Women worldwide spend an average of 4.5 hours each day on unpaid work - cooking, cleaning, feeding the baby. Men devote less than half that much time, according to the OECD.

In the United States, women now financially support 40 percent of homes and tend to take on more domestic chores. They typically spend two hours and 12 minutes on daily housework, while men invest about one hour and 21 minutes into the home.

In an open letter earlier this year, Melinda Gates offered her explanation of the labor division, arguing that no person should feel compelled to fit their stereotypical gender roles - everyone should pursue the life they want, be it work or home-centric.

''This isn't a global plot by men to oppress women,'' Gates wrote. ''It's more subtle than that. The division of work depends on cultural norms, and we call them norms because they seem normal - so normal that many of us don't notice the assumptions we're making. But your generation can notice them - and keep pointing them out until the world pays attention.''