“Birds of a feather flock together” and “opposites attract” are two
contrasting statements dating from the 16th century. Over the past
half century, many researchers have examined the scientific validity of
these two folk beliefs (see Epstein & Guttman, 1984; Watson et al.,
2004). Research along these lines addresses two fundamental questions
about intimate relationships: (1) Is there evidence for systematic couple
similarity? (2) Regardless of overall evidence for couple similarity, is
variation in couple similarity associated with relationship satisfaction?
To answer these questions, previous research has examined a wide
range of domains, which largely fall into three categories: demographic
variables (e.g., age, education, ethnicity, religion), attitudinal domains
(e.g., attitudes, values, interests), and personality domains.