From the end of 2007 to the end of 2009, in states where the economy remained relatively strong, fewer people signed up for Ashley Madison.
There was a lot of variation among the states, and it's easy to think of other possible causes besides economic ones for those differences.
Ashley Madison's marketing campaigns might explain membership increases in some areas, for example. In addition, 74 percent of Ashley Madison's users have a college degree, so a lower concentration of highly educated people might correspond to a smaller target audience for the site. During those two years, Ashley Madison's membership nearly quadrupled in Massachusetts, the state with the highest level of educational attainment, even though the economy there fared relatively well during the crisis.
All the same, in states where the employment level fell further, more people signed up for Ashley Madison. People out of work might find they have more time to pursue an affair. Also, a reduction in family income might spark stress and conflict between spouses.
"It may very well be that in times of distress that one's partner could also be viewed with antipathy, leading one to cheat," said Eric Anderson, a sociologist at the University of Winchester in England who is working as a consultant to Ashley Madison. He also said an extramarital affair might look like an easy way for people to distract themselves from worrying about financial problems.
Other interesting notes from Ashley Madison's data:
• Almost all of the activity on Ashley Madison - around 95 percent - is heterosexual.
• Husbands with 39-year-old wives should be extra nice: Women who are 39 years old are more than four times as likely to sign up for Ashley Madison as women aged 38 or 40.
• About one-third of Ashley Madison's users seek their first affair from three to five years after their wedding, around the time when the first child is born.
• A little more than a quarter of Ashley Madison's users first create an account when their children leave the house for college. Men in this group are generally between the ages of 60 and 65, while women are between the ages of 55 and 58.
There are around 60 million American married couples, according to the Census. Around 13 million people in the United States have created an account on Ashley Madison to date, about three-quarters of whom identified themselves as married or in a committed relationship. Many of them might not have exchanged anything more intimate than a message with a potential lover on Ashley Madison, but the site still offers researchers a massive amount of data to explore.
"For the first time that I'm aware of, we have the ability to peek in on people having an affair, and if that doesn't thrill any researcher interested in human sexuality, I don't know what could," Anderson said.
Separate research by Christin Munsch, a sociologist at Furman University, suggests another reason that adultery and the economy might be connected. After controlling for factors such as a person's income, education and satisfaction in his or her relationship, Munsch found that men who earned very little relative to their wives were much more likely to stray. Perhaps as men lost their jobs during the recession, they might have wanted to compensate for what they felt to be their professional failure by asserting their sexual prowess.
Munsch also found that among very wealthy women, those who made significantly more than their husbands were also more likely to cheat. During the recession, a woman who was highly successful in her career might have been more likely to judge her husband's termination by her own experience and lose respect for him, Munsch said.
Munsch, who is preparing her work for publication, says her research is based on survey data from the Bureau of Labor Statistics. While she has confidence in the survey's methods, Munsch she acknowledges that subjects might have lied to the government's pollsters.
Dishonesty among those surveyed has been an obstacle to research on infidelity. Sociologists and psychologists have long sought to understand how many married people are unfaithful and why they do it, and estimates of the proportion of cheaters based on surveys range widely - from 25 percent to 75 percent of married people.
To be sure, there are limitations on Ashley Madison's data, as well, since it is a particular kind of person who signs up on a dating website for married people. The site's advertising is aimed at well-educated women. Only about 32 percent of all Americans have a college degree, while almost three-quarters of Ashley Madison's users do.