NEW YORK ( MainStreet) — Helping out with the dishes? She says you're a sweetheart. Pitch in with folding the clothes? Best husband ever. But all the chores husbands do to help their wives are causing a serious side effect: less sex.

Couples who divide household chores in more "traditional" ways: he mows the lawn, she does the dishes -- report having more sex than couples who share so-called "men's and women's work," according to a new study co-authored by sociologists at the University of Washington.

Men and women reported having sex about five times, on average, in the month prior to the survey. But marriages in which the wife does all the traditionally female tasks reported having had sex about 1.6 times more per month than those where the husband does all the traditionally female chores.

It's not about money

Do gender roles, work life and income factor in somehow? The researchers say no. Two-income households had the same results -- with similar patterns of sexual frequency relative to the division of household chores -- regardless of whether a spouse worked outside the home.

In addition, a wife's income was unrelated to how often the couple had sex.

"The results show that gender still organizes quite a bit of everyday life in marriage," says co-author Julie Brines, a UW associate professor of sociology. "In particular, it seems that the gender identities husbands and wives express through the chores they do also help structure sexual behavior."

The bedroom barter system

Past studies have reported that husbands received more sex if they did more housework – a kind of bartering system: sex for housework. (Does that really work?) But this new study says prior research did not factor in what types of chores the husbands were doing.

Published in the February issue of the American Sociological Review , the University of Washington study says sex is directly linked to what types of chores each spouse does.

However, husbands shouldn't head out to the garage to "rotate some tires," leaving the cooking, cleaning and shopping to the wife, says lead author Sabino Kornrich. "Men who refuse to help around the house could increase conflict in their marriage and lower their wives' marital satisfaction," he said.

Same old story: Damned if you do, damned if you don't.

Dated data?

The findings come from a national survey of about 4,500 heterosexual married U.S. couples participating in the National Survey of Families and Households from 1992 to 1994. Even though the core data are a bit dated, Brines says that it is unlikely that the division of housework and sex have changed much since then.

The researchers found that husbands, average age 46, and wives, average age 44, spent a combined 34 hours a week on traditionally female chores. Couples spent an additional 17 hours a week on chores usually thought of as men's work.