SURVIVOR TREATMENT SELECTION BIAS IN OBSERVATIONAL STUDIES - EXAMPLESFROM THE AIDS LITERATURE

Unlike patients in a randomized, clinical trial, patients in an observ ational study choose if and when to begin treatment. Patients who live longer have more opportunities to select treatment; those who die ear lier may be untreated by default. These facts are the essence of an of ten over-looked bias, termed ''survivor treatment selection bias,'' wh ich can erroneously lead to the conclusion that an ineffective treatme nt prolongs survival. Unfortunately, misanalysis of survivor treatment selection bias has been prevalent in the recent literature on the acq uired immunodeficiency syndrome. Approaches to mitigating this bias in volve complex statistical models. At a minimum, initiation of therapy should be treated as a time-dependent covariate in a proportional haza rds model. Investigators and readers should be on the alert for surviv or treatment selection bias and should be cautious when interpreting t he results of observational treatment studies.