Anyone who has been happily married probably doesn't need science to tell them that having a loving and supportive partner isn't just great for your private life -- it's great for your career too. But in case you're the least bit skeptical, studies do exist.

"A spouse's personality influences many daily factors that sum up and accumulate across time to afford one the many actions necessary to receive a promotion or a raise," explains Joshua Jackson, a psychology professor at Washington University in St. Louis who led recent research on how the right partner can improve your chances of career success.

How do you build a great, career-supporting relationship? Research can help here too. No study can pinpoint how to find your dream partner, of course, or counsel you through deeply personal rough patches. Luck, kindness, and character will always be the (non-scientific) foundations of great relationships, but that doesn't mean researchers haven't been digging into how partnerships go off the rails for decades in order to offer whatever help they can.

Psychologist and Binghamton University professor Matthew D. Johnson recently gathered all those findings into one book, entitled Great Myths of Intimate Relationships: Dating, Sex, and Marriage. In it, Johnson breaks down the most common false beliefs about relationships that get couples into difficulty, including:

1. Opposites attract.

The opposite actually. "This is a question that relationship scientists, like me, have been studying for decades. In all of the studies there is essentially no evidence people are attracted to those who are different from themselves--much less the opposite of themselves," Johnson told in an email. "We tend to marry people who are from the same social class, have the same values, and share the same interests."

Where does this myth come from? Rather than differences making you a good couple. Being a couple may make you, over time, more different.

"Spouses begin to complement each other over time, even when they start out as quite similar. In other words, couples fall into certain roles in a long-term relationship. Both partners may have started the relationship as being careful with money but perhaps the wife ended up managing the family finances. Flash forward a few years and from the couple's perspective the wife is the one 'always worried about money' and the husband is 'clueless' about the family's finances," Johnson explains.

The takeaway here is probably twofold. If you're looking for love, don't be put off by similarity. Research suggests that marrying someone who is like you in fundamental ways will probably increase your satisfaction with the relationship.

And if you're already partnered up, remind yourself regularly that it's easier to spot differences than appreciate similarities. "When couples come to me for counseling, they never want to talk about how similar they are," Johnson wryly notes. Maybe if you pay more attention to what you have in common, you'll be a bit less likely to need the services of someone like him.

2. Having children will strengthen your marriage.

Nope, being responsible for other lives is actually one of the biggest stressors out there. "I surveyed decades of studies on the psychological effects of having a child to write my book," Johnson notes in a Washington Post op-ed. They all point in the same direction when it comes to how babies affect their parents relationships.

"The relationship between spouses suffers once kids come along. Comparing couples with and without children, researchers found that the rate of the decline in relationship satisfaction is nearly twice as steep for couples who have children than for childless couples. In the event that a pregnancy is unplanned, the parents experience even greater negative impacts on their relationship," Johnson says, summing up a stack of studies.

Johnson isn't aiming to scare couples off reproduction, obviously. "Most mothers (and fathers) rate parenting as their greatest joy," he also writes. But forewarned is forearmed. When you have kids, your partnership is probably going to need effort and re-negotiation to stay strong. "New parents tend to stop saying and doing the little things that please their spouses. Flirty texts are replaced with messages that read like a grocery receipt," cautions Johnson.

3. Living together first makes it more likely that a marriage will work.

This sounds like a completely sensible idea, but the data simply doesn't bear it out. "It turns out that living together before engagement increases the chances of dissatisfaction and divorce down the road," Johnson says. How could that be?

"The current thinking is that couples who move in together for convenience may end up drifting into marriage instead of making a purposeful decision to get married. For example, maybe a couple is already spending several nights a week together and they don't see the reason to write two separate rent checks every month, so they move in together. Then, they're living together for a while and their family starts asking: 'When are you two getting married?' Pretty soon the inertia of their relationship pulls them into marriage as opposed to making a deliberate decision to marry," he explains.

That's one more reason to be annoyed at relatives asking you about your relationship status then. But this insight is also useful. If they know that living together can silently pressure people to move a relationship along, co-habitating partners might think a bit harder about taking things to the next level -- and that could save them serious heartache down the road.

Want more research-backed tips? Here's what one biological anthropologist and expert on the subject (she is also the chief scientific adviser for has to say on the subject of maintaining a long and happy relationship.