Finding truths in clinical medicine: Through the looking glass—cracked

The Episcope. The user looks at the output of the device (level k) and sees the “known” risk difference ( ^kRD) (or any other measure of effect). The known RD results or information transmitted, like light waves through a telescope, from a causal (“etiologic”) RD ( ^aRD) in a target population, through layers of “lenses” and “filters.” Each layer is a distinct domain in which certain types of biases operate, potentially adding additional distortion. It is only by considering the biases introduced at each level that we can determine to what degree ^kRD is an accurate proxy for ^aRD. From Maclure M, Schneeweiss S. Causation of bias: the episcope. Epidemiology. 2001;12:114-122. Used with permission from Lippincott Williams & Wilkins, Baltimore, MD.

A knowledge acquisition device modeled after Kelly et al.⁸ These authors suggest that following the steps in level b leads to an accurate assessment of the truth. Compared with the Episcope, this model may be overly simplistic.