This is the first in a series on why marriage matters to society by HARRY BENSON, research director of the Marriage Foundation.

Since the 1930s, conventional wisdom among researchers has been that marriage tends to start off well but gradually deteriorate.

Yet somehow this has never felt quite right. Yes, we all know older couples who bicker. And we’ve all seen couples sitting in stony silence in a restaurant, having run out of things to say.

But is that really the norm? What about all those sweet old couples we see holding hands and showing each other little kindnesses and affection?

At long last, Paul Amato and Spencer James, two American sociologists and family researchers, seem to have cracked the problem and have produced a brilliant study that explains the previous depressing findings, that fits with people’s more positive and optimistic experience of reality, and really makes sense.

The research, reported in the Sunday Times and others in the UK and by the authoritative Institute for Family Studies in the US, is based on a large data-set of 1,617 married men and women who were questioned every few years between 1980 and 2000 for the US-based ‘Marital Instability over the Life Course’ survey.

Where this differs from previous studies is that the researchers split this group into those who divorced and those who stayed married.

As you might expect, those who divorced on average showed steady declines in their relationship happiness and number of shared activities, and a steady increase in their level of marital discord.

(Happiness was measured by ten questions about different aspects of their relationship, such as love and affection, understanding and sex. Shared activities measured how often they did things together, such as eating, going out, visiting friends and shopping. Discord measured the way they dealt with problems, the extent to which they quarrelled, and whether they ever thought about leaving.)

Here’s the good bit. Among the married couples who stayed together, on average:

Happiness generally started high and stayed that way;
Shared activities declined a little over the first twenty years of marriage but picked up again after that;
Discord showed a steady decline over time.

This makes much more sense than the received but now demonstrably mistaken wisdom that marriage deteriorates over time.

The mistake most studies have made is to look at all marriages as one group. Those marriages that are headed for divorce have dragged the average scores down. And so it appears that marriages – on average – get worse over time.

Isn’t it self-evident that those who stayed together were also the ones who stayed happy? And could this be just an example of ‘survivor bias’?

Not at all. The study explodes the myth that the reason couples argue less and less is only because they have less and less in common, finding themselves trapped in ever-increasing misery and disillusion, but with nowhere else to go.

In fact, the reverse is the case. Couples argue less and less over time, but they also stay happy and end up doing more things together.

What this suggests is that as couples adapt to change over time, whether in taste or personality or circumstances, those positive individual characteristics – such as honesty, kindness, generosity, compromise, trust, ability to communicate – also grow over time giving them a resilience that helps them make their marriage work in all circumstances.