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Schmidt-Pokrzywniak, Andrea; Stang, Andreas
Clinical Epidemiology Unit, Institute of Medical Epidemiology, Biometry and Informatics, Medical Faculty, University of Halle-Wittenberg, Halle, Germany, firstname.lastname@example.org
We read with interest the recent articles about guidelines for reporting observational studies (STROBE) in this journal and others.1–3 We believe that these guidelines are generally very helpful for both the young scientist and the experienced epidemiologist. However, for the revision of the STROBE guidelines it is important that they are critically reviewed, as has been started by Rothman and Poole.4
We would like to offer our own suggestions for revision of the STROBE documents. First, the formula on interaction is incorrect as it now appears in all the STROBE publications3,5,6:
The correct formula is as follows (with +1 rather than −1 in the final term):
Secondly, Vandenbroucke et al3 state that inappropriate inclusion of variables that are in the causal pathway between exposure and disease may introduce bias “unless the aim is to assess how much of the effect is carried by the intermediary variable” (p 824). However, this statistical approach is highly controversial and will be valid only if several assumptions are met.7–9
Clinical Epidemiology Unit
Institute of Medical Epidemiology, Biometry and Informatics
Medical Faculty, University of Halle-Wittenberg
© 2008 Lippincott Williams & Wilkins, Inc.
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