Parenting Interventions: Is Targeting Earlier Better? Combining Individual-Participant (IPD) and Aggregate Multilevel Meta-Analysis

For advancing prevention, it is vital to improve targeting of interventions to at-risk subgroups. We combine two complementary types of meta-analysis to test differential age effects of parenting interventions. Age targeting is salient because of the recent substantial policy and scientific thrust towards early intervention, based on evidence that development is more malleable during sensitive periods. Heckman aggregated data across ages and multiple interventions, claiming greater effectiveness and cost-effectiveness of early vs later interventions. However, his analyses are limited by confounding age with intervention type (e.g. parenting vs. bootcamps), allowing no comparison of similar interventions at different ages. In the field of parenting interventions for conduct problems, investigators have tested age effects across similar interventions, using conventional meta-analysis, but this has yielded mixed findings, and is limited by coding moderators at trial aggregate-level, hence all information is lost about within-trial variability in age. Furthermore, no trials have looked at differential cost-effectiveness by age.

To overcome these limitations, we conducted individual participant data (IPD) meta-analysis of a near-complete set of European randomized trials of Incredible Years parenting intervention (IY;1799 children age 2-10; 14 trials, 6 countries). We used random effects modelling to separate individual from trial-level variation. Where outcome instruments differed, we harmonized data across trials using norm deviation scores for the primary outcome, parent-reported disruptive child behavior. Economic data were harmonized across a subset of 5 UK trials. Our complementary study meta-analysed 150 trials of parenting programs, using robust variance estimation (396 effect sizes; N=16,345, age 2-10) to test whether, at trial aggregate-level, intervention effects on disruptive behavior are moderated by child age; and if developmentally-targeted programs are more effective.

We found that contrary to expectations from the literature, across both methods, there were no effects of age on intervention outcome; economic analyses suggested that cost-effectiveness was greater at older ages. Thus there is potential for return on investment to be higher at older, not younger ages. For examining differential effects, our twin methods are ideal in combining strengths of generalizability across a wider range of interventions and settings in conventional meta-analysis, with the greater power, precision, and, especially, utilization of individual-level age information afforded by IPD. Examining differential cost-effectiveness is novel, and reaches very different conclusions from Heckman, when comparing effects of like-for-like interventions at different ages.