From bad to worse: collider stratification amplifies confounding bias in the “obesity paradox”

Smoking is often identified as a confounder of the obesity–mortality relationship. Selection bias can amplify the magnitude of an existing confounding bias. The objective of the present report is to demonstrate how confounding bias due to cigarette smoking is increased in the presence of collider stratification bias using an empirical example and directed acyclic graphs. The empirical example uses data from the Atherosclerosis Risk in...