Concurrent and longitudinal dyadic polynomial regression analyses of Big Five traits and relationship satisfaction: Does similarity matter?

• Testing trait similarity effects on satisfaction with dyadic polynomial regression analyses only yielded few results.
• Concurrent APIM effects reflected the data equally well compared to more complex dyadic polynomial regression analyses.
• Longitudinal similarity effects emerged for neuroticism and males’ satisfaction and openness and females’ satisfaction.

Being with a well-matched partner seems essential for a happy relationship. However, past research on personality similarity in couples has reported inconsistent findings. The current study employs a dyadic polynomial regression approach to take into account linear and curvilinear associations between similarity and satisfaction. The concurrent results based on data of 237 couples suggest that beyond actor effects for neuroticism, agreeableness, and conscientiousness and partner effects for agreeableness, similarity plays a negligible role for relationship satisfaction. Longitudinally, two similarity effects emerged. First, if partners reported dissimilar neuroticism levels, male partner reported lower relationship satisfaction. Second, if both partners reported modest levels in openness, female partners reported higher relationship satisfaction. Implications for couples are discussed.