It may soon be possible to predict whether your partner is likely to cheat on you, according to research psychologists at Sheffield Hallam and Leicester universities.
Generating a "measure of infidelity" has been a tantalising but elusive prospect for years. This is because the work has focused on attempts to draw conclusions from sociological data, such as whether people from certain backgrounds are more or less likely to be unfaithful.
But now researchers are looking beyond this and are trying to develop a psychological measure of infidelity that focuses on personality types.
Marianne Quick of Sheffield Hallam University said: "While we may know quite a lot about the socioeconomic and demographic background of people conducting affairs, this data has proved to be an unreliable predictor of infidelity, and until now we have not been able to explain why some individuals go ahead while others say 'no'. What we are interested in is the personality-infidelity link."
Identifying subjects for the fieldwork has, perhaps understandably, been an uphill struggle, but Ms Quick, working with John Maltby at the University of Leicester, believes she is close to a breakthrough.
Her research has identified a clear link between infidelity and risk-taking personality types, coupled with an extrovert tendency.
The research, with more than 70 respondents, revealed that the higher people scored on measures of psychoticism or extroversion, the more acts of infidelity they committed.
Ms Quick said those who scored high on psychoticism were typically solitary individuals, often lacking in empathy. They were often risk-takers who tended to live dangerously and seek rewards with little concern for the possible adverse consequences.
They were characteristically gamblers who believed that an element of risk added spice to life, she said. It could be argued that this type of personality was needed to carry out an affair, Ms Quick added.
The finding that extroverts were more likely than others to be unfaithful could be down to their stronger sexual desires and need to engage in varied sexual stimulation. "It seems that extramarital affairs may result from risk-taking based on a gain-and-loss assessment in which people stay or leave a relationship depending on investments made and alternatives offered," Ms Quick said.
For instance, a married man or woman with a home and family would be likely to weigh up the loss of these benefits against the advantages of the affair.
"The difficulty is that people's values differ enormously. And, of course, their previous experience of relationships - maybe going back to childhood - would influence their decision. But our findings seem to suggest that infidelity is not necessarily a capricious and inconsistent event," she said.
One respondent, a 53-year-old male, described why he became unfaithful to his wife and how he deceived himself as well.
He said: "The benefit of having the affair was just that someone was interested in me and wanted to get to know me as well. It was emotional. I would say that the second lady did understand me better, but that was just how it seemed at the time - (she) probably didn't know me better than someone who was married to me for 17 years."
Guilt was a recurring theme in the interviews. A 35-year-old female respondent revealed how she felt "horribly guilty" to begin with - but not for long.
"I felt guilty about not feeling guilty, but sometimes it made me closer to P (her husband) because I even felt sorry for him and more affectionate that this poor guy wasn't doing anything particularly wrong to me - he's done what he has always done," she said.
"But he did make me feel guilty because he had not changed. I changed, I wanted more and he didn't, and I think it probably made me a bit more affectionate towards him."
Another woman described how her affair was "a buzz" to begin with before the guilt set in.
"That night I just wanted to cry my heart out, and I remember holding him in bed, cuddling him and thinking I love him so, so much, I really wish I hadn't done that," she said. "I knew there was no way back and for me there was no way forward either, without telling him, because I betrayed him and betrayed myself.
"I felt like I'd let myself down, and I loved him so much I thought we can go on from this and be stronger. The guilt was unbearable that night, and maybe even the guilt was part of the reason I told him."
Anyone wishing to take part in the research can contact m.quick@shu.ac.uk