[Online dating] sites tend to emphasize similarity on psychological variables like personality (e.g., matching extroverts with extroverts and introverts with introverts) and attitudes (e.g., matching people who prefer Judd Apatow’s movies to Woody Allen’s with people who feel the same way). The problem with this approach is that such forms of similarity between two partners generally don’t predict the success of their relationship.

This condemnation of the “science” of online dating, by Eli Finkel and Benjamin Karney, appeared in yesterday’s New York Times. I read it with great interest, not only thanks to my ongoing (and entirely disinterested) obsession with online dating, but because of its tidy summary of what we do know about the science of compatibility.

My own analysis is much less rigorous, and based on a far smaller data set: my marriage, and the marriages and relationships of my friends. And if there’s one thing I’ve learned from the various breakups I’ve witnessed, it’s that you never really know what’s going on in anyone else’s relationship (which is what makes for frequently astonishing post-breakup revelations). So let’s say that my analysis of what makes for a happy relationship is really mostly based on my own…but since any half-decent social scientist would have predicted that my family history would give me incredibly low odds of a happy marriage, I feel like this relationship formula could be useful to those who are trawling eHarmony and Craigslist for their perfect match. Here’s what I suggest looking for:

1. Common interests: I’d like to tell you that our mostly-harmonious relationship is based on our awesome communications skills, and sure, they’re worth something. But there is just way less to fight about when you both prefer watching The Matrix to The Pianist, when you like both like rainbow bedsheets over white linens, and when you both think that the Apple Store is the perfect place to spend date night.
2. Complementary temperaments: Most couples seem to have one person who is more of a high energy extrovert, and one person who is more of a calm introvert. The high energy person (that’s me) makes sure you are both trying new things, socializing with friends, and having fun; the calmer person (that’s Rob) makes sure you both stay sane, take time for the two of you, and stay grounded. This to me seems the the essential axis on which you should look for a complementary rather than similar mate, though it can be hard to assess online.
3. Common schedule: I have seen a number of happy mixed marriages — you know, between a morning person and a night person. I have no idea when they see each other. (But maybe that’s why they are happy.) Being married to a fellow night-person means that I don’t have to fight for the right to stay up past 10, or apologize for sleeping late on the weekends.
4. Complementary functions: Especially once you have kids, it’s helpful to have a clear division of responsibilities. If you can divide things up via natural affinity rather than horse trading, you reduce a common source of stress and conflict. We like to say that in our house, Rob is the Vice-President of Operations (laundry, dishes, brushing of kid teeth) while I am the Vice-President of Special Projects (vacation planning, seasonal closet purges, school projects). I think I’m getting the sweet deal, but apparently Rob thinks he is too. FTW!
5. Common flaws: Since I am a messy pack rat, a lousy budgeter and a technology compulsive, it might have been wise for me to marry someone who was tidy, good with money, and keen to peel me away from the computer whenever possible. But I would have driven that kind of person completely crazy! So I live in a messy house with a million concurrently-used screens paid for with money that probably should have gone into a retirement savings. You’d probably hate it. That’s why I didn’t marry you.
6. Complementary in common: Maybe you have been thinking, hmm, this is all fine, but why is she misspelling “complimentary”? Actually, that is how you spell this kind of complementary — as in, two things that go well together, as opposed to one thing that is either flattering (a compliment) or free. If you already knew that, or you were delighted to learn it, you should be with someone else who thinks that correct spelling and grammar are incredibly important. If you think this is a totally pointless sixth point, you should make sure not to waste your romantic time on the language nerds of the world, because we will only break your heart when we catch you making some basic error and then not even caring about it.