Negative temperament as a moderator of intervention effects in infancy: testing a differential susceptibility model

A consideration of potential moderators can highlight intervention effects that are attenuated when investigating aggregate results. Differential susceptibility is one type of interaction, where susceptible individuals have poorer outcomes in negative environments and better outcomes in positive environments, compared to less susceptible individuals, who have moderate outcomes regardless of environment. In the current study, we provide rationale for investigating this type of interaction in the context of a behavioral childhood obesity preventive intervention and test whether infant negativity moderated intervention effects on infant self-regulation and weight gain and on two aspects of mothers' parenting competence: parenting self-efficacy and parenting satisfaction. Results showed that infants' negative temperament at 3 weeks moderated intervention effects on some, but not all, outcomes. The intervention led to greater parenting satisfaction in mothers with highly negative infants but did not affect parenting satisfaction in mothers with less negative infants, consistent with a model of differential susceptibility. There was also a trend toward less weight gain in highly negative intervention group infants. In contrast, there was a main effect of the intervention on infant self-regulation at 1 year, such that the intervention group had higher observed self-regulation, across levels of infant negativity. Results support the importance of incorporating tests of moderation into evaluations of obesity interventions and also illustrate that individuals may be differentially susceptible to environmental effects on some outcomes but not others.