Assortative mating — or, in common language, the tendency of birds of a feather to flock together — has long been known to play a big role in how people choose their marriage partners. Traditionally, people have assortatively mated, or sorted themselves, by height, socioeconomic standing, religion — and psychiatric profile. People with depression, bipolar disorder, OCD, ADHD, personality disorders and substance-abuse issues are all more likely to marry other people who either have those problems or have relatives who do. “People are attracted to each other based on their similarities,” say Carol Mathews, a psychiatrist with the UCSF Medical Center who has studied the role of assortative mating in psychiatric disorders. “It’s not necessarily a conscious choice.