Inconclusive evidence for an increasing effect of maternal supportiveness on childhood intelligence in Dunkel et al. (2023): A simulated reanalysis

In a recent study (N = 1075), Dunkel et al. (2023) concluded that maternal supportiveness is important for children's general intelligence. Maternal supportiveness was measured at ages 14, 24, and 36 months while children's intelligence was measured at ages 14, 24, and 36 months and at 4 and 10 years. The effects of maternal supportiveness at time T (β = 0.12), of maternal supportiveness at time T + 1 (β = 0.08), and of the child's intelligence at T + 1 (β = 0.49) on the child's intelligence at T + 2, were all positive and statistically significant when adjusting for one another. However, it is known that such adjusted cross-lagged effects may be biased due to residual confounding and regression to the mean. In the present study, we fitted various models, including latent change score models, on data simulating the data used by Dunkel et al. We found discrepant effects. For example, a positive effect of supportiveness on subsequent increase in children's intelligence (β = 0.04) was accounted for by maternal intelligence (β = 0.01 after adjustment). Another effect indicated that low supportiveness may compensate for having a mother with low intelligence and allow children to achieve the same intelligence as children to more intelligent and supportive mothers (β = 0.34). These divergent findings suggested that it may be premature to assume an increasing effect of maternal supportiveness on children's intelligence. It is important for researchers to bear in mind that correlations, also in superficially more advanced forms like cross-lagged effects, do not prove causality.