Effects of adjusting for instrumental variables on bias and precision of effect estimates.

ABSTRACT: Recent theoretical studies have shown that conditioning on an instrumental variable (IV), a variable that is associated with exposure but not associated with outcome except through exposure, can increase both bias and variance of exposure effect estimates. Although these findings have obvious implications in cases of known IVs, their meaning remains unclear in the more common scenario where investigators are uncertain whether a measured covariate meets the criteria for an IV or rather a confounder. The authors present results from two simulation studies designed to provide insight into the problem of conditioning on potential IVs in routine epidemiologic practice. The simulations explored the effects of conditioning on IVs, near-IVs (predictors of exposure that are weakly associated with o

SUBMITTER: Myers JA 

PROVIDER: S-EPMC3254160 | biostudies-literature | 2011 Dec

REPOSITORIES: biostudies-literature