Soc-Cult-0029-Stock Ruddington Photos/ Flickr/Creative Commons

Tom Smith, the highly respected academic survey researcher, has this to say about extramarital sex: "There are probably more scientifically worthless 'facts' on extramarital relations than on any other facet of human behavior." Given the relentless coverage of the extramarital affairs of Sen. John Ensign and Gov. Mark Sanford, it's worth asking: Just how common is this kind of cheating? And, furthermore, do Americans care?

Smith, who directs the General Social Survey at the National Opinion Research Center (NORC) at the University of Chicago, has spent years steeped in the academic and popular polls on the subject. There is hardly any reliable trend data on the subject before 1988, and what data do exist show little change in the incidence of these affairs over time.

In a 2006 paper Smith reported: "The best estimates are that about 3% to 4% of currently married people have a sexual partner besides their spouse in a given year and about 15% to 18% of ever-married people have had a sexual partner other than their spouse while married."

This is a far cry from the claims of some sex researchers like Sherry Hite, who has posited that 70% of women who have been married for five years or more are having affairs.

According to Smith, the proportion of Americans who have ever had an affair rises from 13% among 18- to 29-year-olds to 20% among those in the mid-life-crisis years, from ages 40 to 49. Then the level drops off.

Perhaps extramarital liaisons are more common among the young, Smith speculates, because they haven't been married long, and they may be more used to multiple sexual partners. Husbands are much more likely than wives to say they are involved in an affair.

When asked whether extramarital sexual relations are always wrong, almost always wrong, wrong only sometimes or not wrong at all, public opinion is uniformly adamant. According to polls, slightly more than 80% of Americans say that extramarital sexual relations are always wrong. The "always wrong" response has actually risen over the past 35 years. In the early 1970s, around 70% of people polled said extramarital sexual relations were always wrong. Today's stricter attitudes could be a reaction against the steady stream of high-profile revelations about the affairs of public figures. Or perhaps we have retreated from the more freewheeling sexual attitudes of the 1960s and 1970s.

To put the views about extramarital sexual relations in perspective, 56% of respondents to the latest NORC poll said homosexual relations are always wrong, and only 26% gave that response about premarital sexual activity.

A new poll from Gallup that asked about 16 behaviors ranging from premarital sex to having a baby out of wedlock to wearing fur found that more people found having an affair morally wrong (92%) than felt that way about any of the other behaviors. Eighty-nine percent of Democrats and 97% of Republicans concurred.

It's difficult to ask people about their own sexual behavior because they are understandably reluctant to admit to personal transgressions. So pollsters often ask about people they know. In 1964, just 24% of people surveyed told Harris interviewers that they knew someone who had an unfaithful wife or husband. That number rose to 30% in 1971.

But in polls conducted by CBS News in 1995 and by Gallup in 2008, a much higher figure (around 55%) gave that response. It's unlikely that behavior has changed that dramatically. But the Harris polls were conducted in person, and people may have been reluctant to discuss infidelity (either in general or their own knowledge of it) with a stranger in their living rooms. The CBS and Gallup questions, on the other hand, were asked in telephone polls, where respondents could be anonymous. More recent polls are also conducted in an environment that may make people more comfortable being honest and in an era in which these kinds of affairs are more publicized.

As for our politicians, the data are remarkably consistent. Pluralities or majorities in most polls say that a politician's extramarital affairs should not disqualify him from serving in office and that a history of engaging in such activity would not affect their vote. All throughout the tawdry drama of public reaction to Bill Clinton's sexual antics, Americans said they could separate his private life from his professional duties. They didn't approve of his behavior, but they based their judgments about him on his performance.

So whatever the frequency of extramarital affairs of everyday people, or how many times Mark Sanford's and John Ensign's escapades dominate the news, it appears that Americans want the private lives of public faces to stay that way.

Karlyn Bowman is a senior fellow at AEI.