By Jason Palmer
Science and Technology reporter, BBC News
A lengthy questionnaire sets out who is best matched to whom
It has often been said that opposites attract but research suggests that initial spark of attraction soon fades and does not make for a long and happy married life.
That is one conclusion from a survey carried out by The Oxford Internet Institute which looked at the habits of 1,000 couples to find the secret of a happy relationship.
It found that couples in different nations have very diverse likes and dislikes when it comes to what keeps them together or drives them apart.
For instance, Britons are the least likely to complain if modern life leaves their partners too tired for sex. Australians are less worried by their spouse being less affectionate and Americans argue more.
The OII survey was carried for online matchmaking service eHarmony which launched in the UK this week. The site claims that it is responsible for 43,000 marriages per year in the US.
EHarmony was founded by professional psychologist Dr Neil Clark Warren and puts potential members through a thorough grilling before their profile is allowed on the site. Those signing up complete a comprehensive questionnaire that plumbs their psyche via more than 200 questions and takes about an hour to complete.
"At the time that we launched in 2000, people were really sceptical that you could bring technology or scientific research to something that had always been attributed in these magical terms to some unknowable quality about why two people connect," says Greg Waldorf, eHarmony's chief executive.
The company's matching approach is based on results from surveys of both couples as well as individuals in each country. The matching process has lead eHarmony to claim that every day on average 118 US couples who met on eHarmony get married - 2% of the total number of marriages.
"What we've shown in our North American market is that we can bring a scientific approach to something that's still a deeply personal and highly emotional process," he said.
But there is not one formula for all couples. Analysis of the data gathered by eHarmony shows that across cultures couples value very different things.
The survey results that drive the matching service identify the major differences in personality types among individuals, and highlight the issues that are most important to couples that describe themselves as happy.
The researchers change their matching model with those personality types and issues weighted differently until the model can successfully predict that the happy couples are a good match.
Paula Hall, a relationship psychotherapist at the UK relationship service Relate, says that she was a fan of online dating and matchmaking services such as Match or Direct Dating as they allow people to meet who otherwise wouldn't cross paths. But, she said, hooking up online is just the start.
"Compatibility is an essential ingredient in relationship happiness, but some differences are inevitable," she says. "How couples manage those differences is the key to long-term success."
With survey data from the US, Canada, Australia, and China also in hand, some cross-cultural trends are evident.
"Notwithstanding the major differences in these global markets, there's a high degree of commonality in how people describe feeling like they're in a successful relationship," Mr Waldorf says.
"Of course there are differences from market to market; the differences we found in the UK we've now adapted in our model in describing how we think about compatibility."
UK couples, the data show, consistently report greater satisfaction with the amount of consensus they experience in their relationship.
Relative to the US, for example, happily married people in the UK tend to agree more on how to make major decisions, how family finances are handled, the division of household tasks, and how to deal with parents and in-laws.
Compared to the US and Australia, UK couples are the least likely to be worried if their partner is regularly too tired for sex.
EHarmony hopes to tap into what makes love work in the UK
In the US, couples put more focus on the interpersonal facets of their relationships, reporting that they laugh together, exchange ideas, kiss, and confide in each other more often. However, they also have more arguments and are more likely to report that their partners annoy them.
In Australia, couples put a lot of stock in working on projects together, and it is the country where couples are least likely to be concerned that their spouse doesn't show enough love and affection.
China presents one significant difference relative to the English-speaking countries.
Couples in the US, the UK and Australia experience a dip in marital satisfaction around the birth of their first child, which Mr Waldorf attributes to a period of adjustment to the change in the relationship.
Chinese couples, by contrast, actually experience a rise in satisfaction, which Mr Waldorf suggests is due to a stronger immediate family support network.
The compatibility measure that ultimately comes from these survey results is totally distinct from similarity, Mr Waldorf says, and couples who are very similar or different are not necessarily compatible.
"We find that 'opposites attract' is not a great long-term kind of compatibility, even though it certainly does drive a lot of initial attraction," he says.