Traditional families today earn more than they did three decades ago — but primarily because they’re working more hours, a recent paper from the Hamilton Project at the Brookings Institution finds.

CATHERINE RAMPELL

Dollars to doughnuts.

Median wages for two-parent families have grown 23 percent since 1975, after adjusting for inflation. The collective number of hours worked by both parents over the course of a year, however, has risen 26 percent. That means their wages haven’t even grown as much as their working hours would imply they should.

The Hamilton Project Annual hours calculated as the average of the middle 10 percent of families. Source: IPUMS CPS 1976-2010.

The additional hours worked by the median two-parent family — 3,500 hours in 2009, compared to 2,800 hours in 1975 — mostly reflect the fact that more women have joined the work force since the 1970s. Men’s annual working hours have stayed relatively constant; women’s, on the other hand, have more than doubled.

These figures may actually overstate the economic improvements in Americans’ lives over the last three decades, too, since they refer to a family structure that is much less common today. The share of men between age 30 to 50 who are married with children was 70 percent in 1975, and only 47 percent today.

Today, there are many more single-parent families, meaning that just looking at two-parent families over time doesn’t give a full picture of what has happened to family incomes.

The median earnings of single-parent families have risen over time, to $16,500. But this number is still less than one-fourth the earnings of a traditional two-parent family. Not only do these households earn less money, but they most likely have more expenses as well, since they require more spending on child care while the single parent works.

That is one argument supporting Nancy Folbre’s proposal that policy makers should look at the market value of what is traditionally known as “women’s work.”

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