PHILADELPHIA (CBS) — It appears that women who feel like they can never get out from under all of that housework can blame….the man they married.

Having a husband creates an extra seven hours a week of housework for women, according to a new study from University of Michigan.

“It’s a well-known pattern,” said economist Frank Stafford, the university’s Institute for Social Research (ISR), who directed the study. “There’s still a significant reallocation of labor that occurs at marriage…men tend to work more outside the home, while women take on more of the household labor. Certainly there are all kinds of individual differences here, but in general, this is what happens after marriage.

And, according to Stafford, the situation gets worse for women when they have children.

The findings are based on 2005 time-diary data from a study on income dynamics that has been conducted since 1968 at ISR.

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Researchers questioned both men and women about the amount of time they spent doing basic household chores in an average week, including cooking and cleaning.

They found that single women in their 20’s and 30’s did the least amount of work around the house, about 12 hours a week, married women in their 60s and 70 averaged 21 hours a week, and married women with more than three children put in an a average of 28 hours of housework each week.

Men showed a somewhat different pattern. Older men did more housework than younger men, but single men did more in all age groups than married men.

But times are changing. The study found that the amount of housework done by women in the U.S. has dropped considerably since 1976 when women averaged 26 hours each week. Meantime, the amount of housework done by men has increased.

“Marriage is no longer a man’s path to less housework,” said Stafford.

The study did not include tasks like gardening, home repairs, or washing the car.