Premium
Modelling treatment‐effect heterogeneity in randomized controlled trials of complex interventions (psychological treatments)
Author(s) -
Dunn Graham,
Bentall Richard
Publication year - 2007
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.2891
Subject(s) - randomized controlled trial , confounding , psychological intervention , alliance , medicine , instrumental variable , average treatment effect , physical therapy , psychology , clinical psychology , statistics , propensity score matching , mathematics , psychiatry , political science , law
We describe instrumental variable (IV) methods for the estimation of the ‘dose’–response effects of psychological interventions in randomized controlled trials in which there is variability in the patients' adherence to the allocated therapy (that is, variability in the actual number of sessions of therapy attended) and also variability in the strength of the therapeutic alliance between patients and their therapists. The effect of the therapy on outcome is assumed to be a function of both the number of sessions attended and the strength of the therapeutic alliance, with no intervention effects in the absence of any sessions attended (an exclusion restriction) and the effect of the strength of the alliance being represented by a multiplicative term (interaction) in the treatment‐effect model. The IV methods that are described allow for: (a) hidden confounding between sessions, alliance andoutcome; (b) measurement errors in the alliance; and (c) that alliance is only measured in those receiving treatment. Three two‐stage estimation procedures are illustrated, and their equivalence demonstrated, through Monte Carlo simulation and analysis of the results of an actual trial. Copyright © 2007 John Wiley & Sons, Ltd.