ANN ARBOR, Mich.—Having a husband creates an extra seven hours a week of housework for women, according to a University of Michigan study of a nationally representative sample of U.S. families.

For men, the picture is very different: A wife saves men from about an hour of housework a week.

The findings are part of a detailed study of housework trends, based on 2005 time-diary data from the federally-funded Panel Study of Income Dynamics, conducted since 1968 at the U-M Institute for Social Research (ISR).

"It's a well-known pattern," said ISR economist Frank Stafford, who directs 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 the situation gets worse for women when they have children."

Overall, the amount of housework done by U.S. women has dropped considerably since 1976, while the amount of housework done by men has increased, according to Stafford. In 1976, women did an average of 26 hours of housework a week, compared with about 17 hours in 2005. Men did about six hours of housework a week in 1976, compared with about 13 hours in 2005.

But when the researchers looked at just the last 10 years, comparing how much housework single men and women in their 20s did in 1996 with how much they did in 2005 if they stayed single versus if they got married, they found a slightly different pattern.

Both the men and the women who got married did more housework than those who stayed single, the analysis showed. "Marriage is no longer a man's path to less housework," said Stafford, a professor in the College of Literature, Science, and the Arts.

For the study, researchers analyzed data from time diaries, considered the most accurate way to assess how people spend their time. They supplemented the analysis with data from questionnaires asking both men and women to recall how much time they spent on basic housework in an average week, including time spent cooking, cleaning and doing other basic work around the house. Excluded from these "core" housework hours were tasks like gardening, home repairs, or washing the car.

The researchers also examined how age and the number of children, as well as marital status and age, influenced time spent doing housework.

Single women in their 20s and 30s did the least housework—about 12 works a week on average, while married women in their 60s and 70s did the most—about 21 hours a 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.

Married women with more than three kids did an average of about 28 hours of housework a week. Married men with more than three kids, by comparison, logged only about 10 hours of housework a week.

Established in 1948, the University of Michigan Institute for Social Research (ISR) is among the world's oldest academic survey research organizations, and a world leader in the development and application of social science methodology. ISR conducts some of the most widely-cited studies in the nation, including the Reuters/University of Michigan Surveys of Consumers, the American National Election Studies, the Monitoring the Future Study, the Panel Study of Income Dynamics, the Health and Retirement Study, and the National Survey of Black Americans. ISR researchers also collaborate with social scientists in more than 60 nations on the World Values Surveys and other projects, and the Institute has established formal ties with universities in Poland, China and South Africa. ISR is also home to the Inter-University Consortium for Political and Social Research (ICPSR), the world's largest computerized social science data archive. Visit the ISR web site at www.isr.umich.edu for more information.