`Half the people who initiate coming to our workshops are men. I was really surprised." Dr John Gottman, Professor of Psychology at the University of Washington, Seattle, is constantly being surprised by the results of his research programmes. Over the past 20 years the agonyaunt, personal-insights-made-general approach to relationship counselling has led to a curious set of received wisdoms. Many of the most important of these are firmly knocked on the head this week with the publication of Why Marriages Succeed Or Fail - And How You Can Make Yours Last, based on 20 years study of 2,000 married couples.

Although its populist title is redolent of the read-this-and-change-your-life school of American publishing, don't be put off. This book should be on every couple's wedding list and its insights are as valuable to people whose marriages are rock solid as those whose marriages are rocky. Dr Gottman's research programme is funded by the US government, concerned at the ever-increasing divorce rate and its knock-on effect on society.

His methodology is unassailable. Before turning to psychology he was a mathematician (with a doctorate at the Massachusetts Institute of Technology). He collects raw data using random sampling, followed by intensive investigation of the physiological responses of volunteer couples using cameras and electrodes. The reason men are so willing to become involved with his research programme is that they trust him, comfortable that his research is science - rather than the terrain of what they tend to perceive as mumbojumbo psycho-babble land. From this numerically classifiable data it has been possible to make a mathematical model showing how a couple interacts. Gottman's work falls into two categories: objective analysis - why longstanding marriages have survived; identification of the factors triggering marital breakdown - and then a second group of studies working with couples who want to repair marriages that are in crisis.

"This really involves trying to change people," he explains. "After all these years we have a pretty good idea of how to help couples and a pretty good idea of what's involved based on the predictions." Currently, Dr Gottman has seven programmes running. One has been going for 15 years. Volunteers include couples who have been married up to 60 years.

The most recent programme is at the other end of the spectrum: 250 newlyweds will be tracked as long as the programme keeps going.

Sex, it turns out, is neither what keeps a marriage together nor what tears it apart. Although extra marital affairs are popularly cited as the major reason for divorce, they are, Gottman believes, simply a symptom of drifting apart, "the deterioration of the friendship in the marriage".

Similarly extra-marital affairs are not usually about sex at all, he believes. "They're really about friendship, about feeling somebody really likes you, cares about you, and finds you interesting. And people are most vulnerable to that when it's not happening in the marriage."

Of course, the friendship element of a marriage is all to do with communication: the analysis of marital communication, both verbal and non-verbal, and the correlation between the two, is what lies at the core of Gottman's research.

Yet successful communication in a marriage need not necessarily mean the Woody Allen talking-everything-through approach. Nor are rows a bad thing - indeed, Dr Gottman believes they are an essential ingredient for a thriving marriage. He equates a marriage to a complex eco-system that without predators (negativity) would become asphyxiated, stifling the possibility of change and growth.

Even from the early days of a relationship when all seems to be going well, how couples handle conflict is a major indicator of whether the marriage will survive. Complaint - which Gottman says is OK, indeed necessary - can all too easily escalate into criticism, followed swiftly by contempt. Yet much of this negative behaviour can easily be rectified, Gottman believes, and his workshops appear to prove it.

"One of the things that we found really interesting, is how couples repair negativity. Let's say they're going through a bad stretch and they're distant with each other. All couples make attempts to repair the relationship when that happens. For some couples the repair attempts work, and for some couples they don't. We had been thinking along the lines of, maybe there's a form of words, some magic way of saying it. But it turns out that there's nothing within the resolution-of-conflict discussion that predicts whether a repair attempt will work or not work. What predicts it is really something entirely different. It's really how the couple interacts when they're not conflicting."

This can range from shared humour to shared memories to simple acknowledgement of the other's concerns. "It's really the nature of the friendship between husband and wife that predicts it - the very mundane part, the everyday kinds of things; even down to the way they read the Sunday papers." Dr Gottman's prediction level of whether a marriage will survive or fail is now a staggering 93 per cent accurate.

Crucial to the success of a marriage is that both partners share the same approach. Those who like a good row and a passionate making-up afterwards can build as strong a marriage as those who rarely say boo to one another. As long as they are both operating under the same rules of engagement, and as long as the ratio of good times to bad remains a regular 5:1.

"That was a surprise," Gottman admits. "I had no idea it was going to be that high." He was expecting around 100:1. Another surprising finding is that the key factor in what makes a marriage work is the man. Although it is usually the woman who sees the success of the marriage as her responsibility, explains Dr Gottman, successful marriages are always those where "emotionally intelligent" husbands are "making maps of their wives' psychological world".

`They know what their wives are concerned about, they know the names of their wives' friends, they know the people in their wives' lives who are pains in the neck. They know something about their wives' hopes and dreams and fears. It's a matter of respect and honouring their wives. One of my friends, a Mormon bishop said: `I figured out one day that even though it's as much work for me to put the toilet lid down as it is for her, if I do it I win an enormous amount of points in this marriage'." In Seattle, as in Dublin, as in Donegal, it's the same old litany of irritations: toilet seats, toothpaste caps and, of course, housework and sex.

She doesn't get enough help with the housework. He doesn't get enough sex. But Gottman has discovered that the two are intimately connected. The happiest marriages are those where the husband shares the housework.

"It says `I don't belittle what you do. I respect you'. The key thing is honouring the woman. It is always men who belittle women's dreams. And women are very quick to belittle their own dreams and to give them up for the sake of the relationship.

"What emotionally intelligent men are doing is honouring their wives' dreams. And that is the most critical thing. Because the dreams really provide meaning."

A wife who feels respected and cherished, he has discovered, is more inclined to express her sense of warmth and validation in the way most husbands seem to want, than one who is treated like a chattel. It's as simple as that.

Why Marriages Succeed Or Fail - And How You Can Make Yours Last by John Gottman, is published by Bloomsbury. Price £9.99 in the UK.