A Within-Person Examination of the Family Stress Model: Family Income, Parental Distress, and Child Mental Health.

The Family Stress Model (FSM) is a key framework explaining the relationship between family income and child mental health. However, most studies examining the FSM are cross-sectional and do not clearly distinguish within- from between-person effects, which limits robust inferences about how family income affects child mental health at the within-person level. This study addressed this gap by applying a Random Intercept Cross-Lagged Panel Model to data from the nationally representative UK Millennium Cohort Study, focusing on children aged 3, 5, 7, 11, and 14 (N = 11,845; ~49.9% female). Findings revealed that within-person decreases in family income were associated with subsequent increases in internalizing problems for boys from ages 3 to 5 and for girls from ages 7 to 11. Further, income was associated with externalizing problems indirectly but only among girls and only through maternal, not paternal, distress. Together, these findings suggest that within-person FSM processes operate in gender- and outcome-specific ways within families. Interventions may benefit from considering both child and parent gender, with maternal mental health as a particularly relevant target during economic hardship.