In his seminal novel, "Anna Karenina," Tolstoy remarked that "Happy families are all alike; every unhappy family is unhappy in its own way." His observation, that it takes the avoidance of flaws to have a successful family (or an experiment), has become adapted by statisticians and ecologists alike, even being deemed the "Anna Karenina principle."

When it comes to marriages, a study from the University of Tennessee found something similar: happy couples tend to argue the same way, or rather, they strategically choose to only argue about problems that have a concrete or easy solution.

The multi-method, two-sample investigation published in the journal Family Process compared couples in their mid- to late-30s to couples in their early 70s. All were self-described as happily married, and were asked to rank their least and most serious issues. Both samples ranked jealousy, religion and family as the least serious, while intimacy, leisure, household, communication and money were ranked as the most serious — including health for the older couples.

As researchers observed the couples discussing marital problems, it became clear that both married groups chose their battles wisely. "Happy couples tend to take a solution-oriented approach to conflict, and this is clear even in the topics that they choose to discuss," said lead author and associate professor Amy Rauer.

For instance, the couples focused on issues with a resolvable solution, like how to spend leisure time or divvy up household chores. "Being able to successfully differentiate between issues that need to be resolved versus those that can be laid aside for now may be one of the keys to a long-lasting, happy relationship," concludes Rauer.

Happy wife, happy life?

older couple embraces man in wheelchair A marriage can help you live longer — as long as it's a happy, healthy one. (Photo: Pormezz/Shutterstock

It's been shown that being in a healthy relationship can help you live longer, too. From cardiovascular disease to depression to cancer, studies show that happy marriages play a valuable role in health issues, and encourage healthy behaviors like a healthy diet and staying socially active. But not just any marriage will do, and it changes depending on gender. Men benefit more from marriage, while women are especially vulnerable to a bad marriage. Psychiatrist Sudeepta Varma tells WebMD: "We now know that depression, obesity and hypertension can all result from women suffering in unhappy marriages."

So how does one keep a happy marriage, well, happy? It could be in your genes. Research from the Yale School of Public Health suggests that happily married couples shared a common strand — specifically, a genetic variation known as the GG genotype within the oxytocin gene receptor. Couples who reported the most domestic bliss had more of the gene, aka OXTR rs53576, which is also linked to qualities found in good people, like empathy and emotional stability.

Of course, not every study suggests that marriage leads to eternal happiness and endless fulfillment in life. Dr. Bella DePaulo believes many scientists are biased when it comes to proving that marriage makes you happier. The author of "Singled Out" and an advocate for singles everywhere states her case in a blog for PsychCentral: "All of these unsuccessful attempts to make married people look better should be more than enough to keep other scholars and journalists from jumping off the deep end with their fortune cookie proclamations, 'Get married, get happier.' But sadly, they aren't."

DePaulo declares that most of these marriage studies are too limited in their scope: only those who got married and stayed married were included in the studies she references, and that comparing stay-married people to stay-single people is simply unfair. They are different groups of people with different motivations in life — and let's not forget that American policymakers also treat married people better with goodies like tax breaks and health insurance benefits. Too many factors go into a married or unmarried person's state of happiness that make it difficult, if not impossible, to determine if marriage alone makes one live happily ever after.

Whether you're married or not, all healthy relationships require upkeep and attention. Good marriages don't just happen out of nowhere, and neither do good friendships. Do your homework and continue the research with these 5 books on more meaningful relationships.

This is how happy couples argue
A new study from the University of Tennessee looks at the multitude of ways and topics married couples argue about, with some not-so-surprising results.