(Cheating is rarer than you think — but it happens.Timothy Marsee/Flickr)

Humans are notorious for thinking they're better than everyone else.

When asked to rate themselves on attractiveness, intelligence, driving ability — you name it — they consistently say they're above average, which obviously isn't mathematically possible.

So it makes sense that people also believe their relationships are healthier than other folks'.

Specifically, people think their own romantic partner has a much lower chance of cheating than the average member of the opposite sex.

That's according to recent research, cited on Science of Relationships, from the University of Calgary and McMaster Children's Hospital. For the study, researchers recruited about 200 university students who'd been involved in heterosexual dating relationships for at least three months.

Those participants filled out an online questionnaire related to their beliefs and expectations about infidelity. (The researchers note that they didn't explicitly define the term "infidelity," so participants were left to use their own interpretations.)

Participants reported that they believe there's about a 42% chance that the average person of the opposite sex either has cheated on their partner or will do so at some point.

But when it came to their own partners, participants estimated that there was about a 5% chance that their partner had already cheated on them and about an 8% chance that they would cheat on them in the future.

So how many participants said they'd actually gone and done it — cheated on their partner? 9%.

Interestingly, even though these couples were dating, and not married, they were just as confident (some might say delusional) in the stability of their relationships as married couples surveyed in other studies.

These findings jibe with other research that found, even after years of dating, couples don't know each other nearly as well as they think they do. So you might think everything is peachy keen in the relationship, when in fact your partner's feeling lonely or frustrated.

Perhaps the most important insight to come out of this research is that even though nearly every person surveyed said it was important that their partner doesn't cheat on them, fewer people said they'd talked about infidelity with their partners.

Less than two-thirds had talked about what constitutes cheating, but even fewer said they'd reached an agreement with their partners about it.

Maybe we hedge the subject because it doesn't occur to us that our partner could possibly stray; or maybe it's because we're afraid of what we'll find out when we broach the topic. Either way, it helps to remember that your partner, like everyone else's partner, is human, and there's a chance — albeit a small one — that they'll be unfaithful at some point.