Instrumental variables and interactions in the causal analysis of a complex clinical trial
Bond SJ., White IR., Sarah Walker A.
AbstractWe consider the application of instrumental variable techniques in a longitudinal clinical trial in paediatric HIV/AIDS, with a substantial degree of non‐compliance to randomized treatment (Nelfinavirversusplacebo) and with left censoring of the outcome variable (HIV RNA concentration). We consider in detail the assumptions and implications behind the inclusion and exclusion of interactions between randomized arm and baseline covariates in modelling actual treatment received, and between treatment and baseline covariates in modelling outcome. Estimated treatment effects were sensitive to inclusion of interactions, and we show how such sensitivity can be explored and explained. Copyright © 2006 John Wiley & Sons, Ltd.