Clarifying the link between psychological need satisfaction and positive affect: Longitudinal within-person tests for bi-directional influence in two cultures

Positive affect is often considered the "hallmark of well-being," associated with better health, longevity, and success. Self-determination theory (SDT) proposes that satisfying three basic psychological needs for autonomy, competence and relatedness (BNS) fosters optimal functioning, thriving, and positive affect. Meanwhile, broaden-and-build theory suggests that positive emotions predict future psychosocial resources such as need satisfaction. Previous research on the BNS-positive affect link has not sufficiently established to what extent changes in BNS precede changes in positive affect or vice versa. We tested this in two 3-wave longitudinal studies, conducted over 2 years in the UK (Study 1: N = 958) and over 2 months in Latin America (Study 2: N = 1200). Bivariate latent trait-state-occasion models revealed that within-person fluctuations in BNS significantly predicted subsequent fluctuations in positive affect in both studies, but fluctuations in positive affect predicted subsequent fluctuations in BNS only in Study 2. These findings consistently support SDT predictions, whereas they only partially support broaden-and-build theory predictions, helping to clarify the likely causal relations between BNS and positive affect.