Selecting on treatment: a pervasive form of bias in instrumental variable analyses.

ABSTRACT: Instrumental variable (IV) methods are increasingly being used in comparative effectiveness research. Studies using these methods often compare 2 particular treatments, and the researchers perform their IV analyses conditional on patients' receiving this subset of treatments (while ignoring the third option of "neither treatment"). The ensuing selection bias that occurs due to this restriction has gone relatively unnoticed in interpretations and discussions of these studies' results. In this paper we describe the structure of this selection bias with examples drawn from commonly proposed instruments such as calendar time and preference, illustrate the bias with causal diagrams, and estimate the magnitude and direction of possible bias using simulations. A noncausal association between the

SUBMITTER: Swanson SA 

PROVIDER: S-EPMC4312427 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature