AbstractParenting programmes are the most effective intervention to change persistent child antisocial behaviour and are widely used, but little is known about the mechanisms through which they work and hence how to improve them. This PhD project aims to bridge this gap by performing formal mediation analyses partitioning total effects of parenting programmes on child outcome into indirect effects (mediated through aspects of parenting) and direct effects (non-mediated effects). This thesis focuses on further developing methods for mediation analysis to cover complex scenarios and applies them in three trials (SPOKES, CPT and HCA) of parenting programmes.
This project improves traditional methods for trials that assume no putative mediator-outcome confounding in three ways: Firstly, the mediator-outcome relationship is adjusted for observed confounding variables. The newly developed MI-BT method facilitates the application of Multiple Imputation to handle missing data and the use of linear mixed models to reflect trial design, and generates non-parametric inferences via a bootstrap approach. The application of this method to the SPOKES trial showed statistically significant indirect effects for two mediators (parental warmth and criticism). Secondly, the MI-BT method is extended to combine with instrumental variables method and become the IV-MI-BT method which allows for unmeasured confounding of the mediator-outcome relationship in the presence of missing data. The application of this method to the SPOKES trial showed that while IV estimators of mediation effects were similar in value compared to MI-BT estimates, their confidence intervals were inflated. Finally, methods were further developed to enable pooling of individual participant data from multiple trials and so provide for potentially more precise and more generalizable mediation analyses. A framework for systematically conducting such an IV-MI-BT IPD meta-mediation analysis is described. Meta-analysis of the three contributing trials did not detect any evidence for between-trial heterogeneity in mediation effects of interest. Pooling of the studies resulted in smaller and non-significant overall indirect effect estimates and provided a considerable precision gain compared to the SPOKES only analysis.
|Date of Award||2015|
|Supervisor||Sabine Landau (Supervisor) & Stephen Scott (Supervisor)|