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Instrumental variables and interactions in the causal analysis of a complex clinical trial
Author(s) -
Bond Simon J.,
White Ian R.,
Sarah Walker A.
Publication year - 2006
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.2644
Subject(s) - covariate , censoring (clinical trials) , instrumental variable , randomized controlled trial , causal inference , nelfinavir , econometrics , outcome (game theory) , medicine , clinical trial , statistics , human immunodeficiency virus (hiv) , mathematics , mathematical economics , family medicine , antiretroviral therapy , viral load
We 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 (Nelfinavir versus placebo) 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.