Almost any married couple that has been together long enough will have heard the jokes about the seven-year-itch - the widespread idea that happiness in a relationship decreases after that period, and 'marital wanderlust' kicks in.
The term has been around for a long time, having been coined by the hugely popular 1955 Marilyn Monroe film of the same name, and the publicity for the film stated that seven years was the average length of a failed marriage in North America at the time.
Ask most people how the situation today compares with the 1950s, and there is a widespread assumption that marriages don't last as long as they used to. Interestingly, however, the statistics clearly show that the opposite is true. In the UK, the typical failing marriage now lasts almost three years longer today than it did 20 years ago.
According to the ONS, the average divorce now happens after 11.6 years, and this has been steadily growing - in 1985, the average divorce happened after just 8.9 years. At JMW, the average for the couples that come to us for help with their divorce arrangements now stands at 12 years.
So what are the factors behind this surprising trend?
A compelling theory for the rapid increase in duration we have seen in the past five years is that the recession is a major contributing factor, with couples putting their divorce plans on hold until their financial situation begins to look up.
A more fundamental consideration is that the overall divorce rate has risen significantly over the past two decades and the fact that a greater proportion of marriages now end in divorce has inevitably changed the profile of the average divorcee.
So-called 'silver splitters' are a good example. There isn't the same stigma attached to divorce that there has been in the past and this, combined with longer life expectancy, is boosting the number of divorces among older people, boosting the average age.
Cohabitation before marriage has also pretty much become the norm, where 30 years ago it was considered unusual or even taboo. Today, couples often wait until many years into their relationship before getting engaged, with many starting families before tying the knot. For many couples, the wedding day now represents a celebration and continuation of a relationship that's already very well established. The result is that a large number of pairings that really weren't meant to be - and which would once have resulted in a divorce - now end before the wedding takes place.
Ultimately, it could be that what the statistics reveal says more about changes in society's attitude to marriage than it does about modern couples' willingness to fight through issues in their relationships.
It's possible that there is still some truth in the notion that many couples begin to get itchy feet after a period of seven years - and the debate will continue among psychologists about the complex causes of this phenomenon.Suggest a correction