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UNIDENTIFIED WOMAN #1: Fifty-two.

UNIDENTIFIED WOMAN #2: Four-hundred-and-fifty-three.

UNIDENTIFIED MAN #1: Twenty-five.

RACHEL MARTIN, HOST:

Time for some number crunching from our data expert, Mona Chalabi of fivethirtyeight.com. She has given us this number of the week.

UNIDENTIFIED WOMAN #3: Thirty-seven million.

MARTIN: That is the estimated number of users of Ashley Madison. It's an online site that makes infidelity as easy as posting an online profile. Last week, hackers said they had stolen data from the company and threatened to release all customer records. The hack made us wonder just how many people out there cheat and what motivates them. Lucky for us, Mona Chalabi is here to sort through the numbers on infidelity. Hey, Mona.

MONA CHALABI, BYLINE: Hi, Rachel.

MARTIN: All right, well, what do we know about how many people cheat? And is this something people are actually honest about when asked by pollsters or researchers?

CHALABI: The most recent research on this suggests that people are actually pretty willing to be honest and confess when they're asked anonymously. In May this year, the polling company YouGov surveyed about a thousand Americans. And they found that 21 percent of men and 19 percent of women admitted that they had cheated on their partners. But it's also worth mentioning that about another 7 percent said they would prefer not to answer the question. So you can read into that what you will.

MARTIN: OK, but still, 1 in 5 Americans, that seems like a lot. Does any research out there tell us about who is more likely to cheat and why?

CHALABI: It's probably easiest to start off with age because there was a study last year that actually used Ashley Madison data to get at this question. But just to be clear, this wasn't part of the leak. This was just a kind of separate study. And this data was obtained with the consent of Ashley Madison's owners. So instead of looking at age groups, the researchers looked at specific ages, each individual year, and found that men who were nine-enders - that means men who were 29, 39, 49, or 59 - were much more likely to be on the site looking for extramarital affair than people who weren't about to begin a new decade of their lives. Eighteen percent more of them were on the site than what you'd expect by chance alone. It's also worth noting - in fact, I think it's really crucial to note - that dating sites don't verify the age of users. So maybe this data is a little bit flawed if those men were kind of fibbing about their age to just knock themselves down to a decade lower.

MARTIN: Yeah, right 'cause that's what we do when we're kind of fudging our age. So it's people on the cusp of some kind of big perceived life change, maybe.

CHALABI: Exactly, yeah.

MARTIN: How does that break down by gender?

CHALABI: When asked, have you thought about cheating, 28 percent of women say yes compared to 41 percent of men.

MARTIN: It's more complicate than just age and gender though, right? I mean, I remember you and I talked a while ago about women who earn more than their partners. And you found that men who are financially dependent on these women are more likely to cheat on them. So we know money comes into it as well - other factors, Mona?

CHALABI: Yeah. There's definitely quite a few. And we know that personality comes into it a little bit. It's kind of difficult to build up a specific profile of exactly who a cheater is. If that was the case then I think we would find dating a lot easier. But we do have some research on this again. So a 2011 study published in the Archives of Sexual Behavior found about 1 in 5 of the thousand people in heterosexual couples they interviewed had cheated. But what it did was it took a closer look at those individual to see what factors were most likely to predict their sexual infidelity. It found that for both men and women, sexual personality characteristics - so that's things like being adventurous and not having performance anxiety - were far more important than demographic stuff, like marital status or religiosity, when it comes to actually predicting whether or not someone's going to be faithful.

MARTIN: OK, so we've been talking about heterosexual couples here. Any research out there about same-sex or bisexual couples?

CHALABI: Not much. This is something I run into all the time. So much of the research is just focused on heterosexual couples. But I did find a 2012 study in the Journal of Marital and Family Therapy. And what they did was they looked at the way that people felt about infidelity. And it found that all participants, regardless of sexual orientation - because they did include different couples in there - found that sexual infidelity elicited more distressing feelings actually than emotional infidelity.

MARTIN: Emotional infidelity - that brings up another question. Does some of this have to do with how people define cheating, Mona? I mean, does there have to be a sexual relationship to constitute cheating for most people?

CHALABI: Not for everyone, actually. And that's what's really, really interesting. There are clear differences between men's and women's perceptions of this. So 76 percent of women, when asked, felt that it was cheating to send flirty messages to someone else. But only 59 percent of men think the same. Now, when it comes to kind of more extreme examples, like having a one-night stand, the genders tend to agree. So 93 percent of women think a one-night stand is cheating, and 91 percent of men think the same. But, what's interesting is actually when it came to being asked, how would you feel if your partner had shared deep, emotional, intimate informational with someone else, people basically felt the same whether that had occurred online or off-line, which is one reason why I'm pretty sure that Ashley Madison's users aren't feeling too great right now that their information is being held by a third party that's threatening to release it.

MARTIN: Mona Chalabi of fivethirtyeight.com. Thanks so much, Mona.

CHALABI: Thanks, Rachel.