Familial Transmission of Personality Traits and Life Satisfaction Is Higher Than Shown in Typical Single-Method Studies

Personality trait similarity among ordinary relatives is surprisingly low, with parent-offspring and sibling-sibling correlations usually being r ≤ .15. We explain why these correlations are distorted in typical single-method studies and argue that this issue can only be addressed with multi-method designs. We also explain why non-twin relative comparisons can provide a more generalizable way of estimating (additive, narrow-sense) heritability than the better-known twin comparisons. In a sample of parent-offspring (Npairs = 522), sibling-sibling (Npairs = 388), and second-degree relative pairs (Npairs = 476), who rated their Big Five personality traits and life satisfaction and were each rated by an independent informant (Nparticipants = 2,258 + informants), we found that parent-offspring and sibling trait correlations were about a third higher than typically shown (r ≈ .20). Based on the ordinary relative comparisons, the heritability of personality traits and life satisfaction was around 40%, up from about 26% typical in self-report studies. Life satisfaction was as heritable as personality traits, with about 80% of the genetic variance shared with neuroticism, extraversion, and conscientiousness. About half of life satisfaction’s phenotypic correlations with neuroticism and extraversion and all its correlation with conscientiousness were accounted for by shared genetic factors. Using data from a larger relatives sample with only self-reports (Nparticipants = 32,004; Npairs = 24,118), we provide further evidence that growing up together does not make people more similar. Additionally, the findings were consistent for both aggregate traits and individual items. Only multi-method designs can reveal traits’ true similarity among relatives, and genetic and environmental transmission.