5 Aims

The aim of this thesis was to explore methodological challenges that impact the evaluation of psychological treatments in general but also gambling treatment trials specifically. The first two studies discuss important methodological issues that researchers tend to overlook, and the issues are investigated empirically using Monte Carlo methods. The results from Study I and II are then applied to answer the clinical research questions in Study III and IV. Specifically, Study I investigates the consequences of ignoring therapist effects in longitudinal data. Study II investigates the challenges of estimating treatment effects in gambling studies using gambling expenditure as an outcome. Study III applies and extends the work in Study II to investigate how concordant gamblers and their concerned significant others are in their reports of gambling losses. Study IV applies the results from Study I, II, and III to investigate the effects of an internet-delivered program aimed at the CSOs of treatment refusing gamblers.