On confounders: known and unknown.
Weiner
Bradley K
BK
Division of Spinal Surgery, The Methodist Hospital, 6550 Fannin Street, Suite 2500, Houston, TX 77030, USA. bkweiner@tmhs.org
D002986:Clinical Trials as Topic; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D006801:Humans; D012107:Research Design