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Epidemiology:
doi: 10.1097/EDE.0b013e31816c4286
Letters

Measures of Biological Interaction and the STROBE Statement

Schmidt-Pokrzywniak, Andrea; Stang, Andreas

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Clinical Epidemiology Unit, Institute of Medical Epidemiology, Biometry and Informatics, Medical Faculty, University of Halle-Wittenberg, Halle, Germany, andrea.schmidt-pokrzywniak@medizin.uni-halle.de

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To the Editor:

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:

Equation (Uncited)
Equation (Uncited)
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The correct formula is as follows (with +1 rather than −1 in the final term):

Equation (Uncited)
Equation (Uncited)
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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

Andrea Schmidt-Pokrzywniak

Andreas Stang

Clinical Epidemiology Unit

Institute of Medical Epidemiology, Biometry and Informatics

Medical Faculty, University of Halle-Wittenberg

Halle, Germany

andrea.schmidt-pokrzywniak@medizin.uni-halle.de

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REFERENCES

1.von Elm E, Altman DG, Egger M, et al; STROBE Initiative. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Epidemiology. 2007;18:800–804.

2.Tuma RS. Statisticians set sights on observational studies. J Natl Cancer Inst. 2007;99:664–665.

3.Vandenbroucke JP, von Elm E, Altman DG, et al; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. Epidemiology. 2007;18:805–835.

4.Rothman KJ, Poole C. Some guidelines on guidelines: they should come with expiration dates. Epidemiology. 2007;18:794–796.

5.Vandenbroucke JP, von Elm E, Altman DG, et al; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. PLoS Med. 2007;4:e297.

6.Vandenbroucke JP, von Elm E, Altman DG, et al; STROBE Initiative. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration. Ann Intern Med. 2007;147:163–194.

7.Cole SR, Hernan MA. Fallibility in estimating direct effects. Int J Epidemiol. 2002;31:163–165.

8.Kaufman JS, Maclehose RF, Kaufman S. A further critique of the analytic strategy of adjusting for covariates to identify biologic mediation. Epidemiol Perspect Innov. 2004;1:4.

9.Petersen ML, Sinisi SE, van der Laan MJ. Estimation of direct causal effects. Epidemiology. 2006;17:276–284.

© 2008 Lippincott Williams & Wilkins, Inc.

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