By Jonathan Amos
BBC News Online science staff, in Seattle
Michael Harris and Andrea Rodgers met on the 4th of July last year and will marry on Independence Day this year. They're an American couple very much in love.
Michael and Andrea: 'we know we're going to be together forever'
"Yes we are," says Andrea, a trainee lawyer. "Absolutely - sickeningly so," adds Michael, who is a few years older than his bride to be.
But are they really a perfect match? The BBC took them to a research centre at the University of Washington in Seattle that has been dubbed the "Love Lab".
Its real name is the Relationship Research Institute. It is here that scientists say they have created a mathematical model that can tell which marriages are doomed to end in divorce.
Psychologist John Gottman and applied mathematicians James Murray and Kristin Swanson claim their predictions have 94% accuracy - and this after viewing just the first few moments of a conversation about an area of marital contention.
Lies and videotape
Subjects brought into the lab like Michael and Andrea have to fill out questionnaires to identify their personality types.
They are then hooked up to equipment to monitor physical and emotional responses during a discussion on a thorny issue such as money.
Swanson goes through the data. She used to be sceptical about the idea of an equation for love.
"There's quite a bit more to it than just maths," she said. "When I initially started working on this, I thought there was no way you could quantify anything like this. It didn't make any sense to me whatsoever.
"But across four different studies now we've been able to find for about 500 different couples that we can predict their outcome with over 90% accuracy."
The model was developed using data collected from a mountain of videotaped conversations between couples. Physiological data, such as pulse rates, also was collected and analysed.
The spiky conversations are said to reflect underlying problems a couple have and that is why the model is so predictive.
"Before this model was developed, divorce prediction was not accurate," Gottman said, "and we had no idea how to analyse what we call the masters and disasters of marriage - those long-term happily married and divorced couples."
The key turned out to be quantifying the ratio of positive to negative interactions during the talks.
The magic ratio is five to one, and a marriage can be in trouble when it falls below this. The mathematical model charts this interaction into what the researchers call a "Dow-Jones Industrial Average for marital conversation".
"When the masters of marriage are talking about something important, they may be arguing, but they are also laughing and teasing and there are signs of affection because they have made emotional connections," Gottman said.
"But a lot of people don't know how to connect or how to build a sense of humour, and this means a lot of fighting that couples engage in is a failure to make emotional connections. We wouldn't have known this without the mathematical model."
As Andrea and Michael wait for their numbers to be crunched, are they nervous?
"I'm confident, we'll pass," laughs Michael. Andrea adds: "That conversion was just us - we know we're going to be together forever, so we just hope the study says the same thing."
And it seems the Love Lab agrees. Gottman has good news. "The prognosis is very good. We predict you will have a very good relationship - a very real relationship," he tells them.
"What we're trying to do is really understand what makes relationships work. And once people understand that, we can help people build romance and passion."
Gottman and his colleagues described their work on Thursday to the annual meeting of the American Association for the Advancement of Science held this year in Seattle.