Some couples in the experimental group actually did manage to double the rate of intercourse, and on average there was a 40 percent increase.

This did not make them happier. In fact, their well-­being declined, especially in measures of energy and enthusiasm, as did the quality of the sex. Both men and women reported that the additional intercourse wasn’t much fun. The results surprised the researchers — but they probably shouldn’t have, according to George Loewenstein, a professor of economics and psychology at Carnegie Mellon, who led the study.

‘‘It seems that if you’re having sex for a reason other than because you like and want sex,’’ he says, you may undermine the quality of that sex and your resulting mood.