To Adjust or Not to Adjust? When a "Confounder" Is Only Measured After Exposure.

ABSTRACT: Advice regarding the analysis of observational studies of exposure effects usually is against adjustment for factors that occur after the exposure, as they may be caused by the exposure (or mediate the effect of exposure on outcome), so potentially leading to collider stratification bias. However, such factors could also be caused by unmeasured confounding factors, in which case adjusting for them will also remove some of the bias due to confounding. We derive expressions for collider stratification bias when conditioning and confounding bias when not conditioning on the mediator, in the presence of unmeasured confounding (assuming that all associations are linear and there are no interactions). Using simulations, we show that generally neither the conditioned nor the unconditioned estimat

SUBMITTER: Groenwold RHH 

PROVIDER: S-EPMC7850592 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature