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J Epidemiol Community Health. 2014 Nov;68(11):1096-100. doi: 10.1136/jech-2014-204195. Epub 2014 Jun 12.

Placing epidemiological results in the context of multiplicity and typical correlations of exposures.

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Center for Biomedical Informatics, Harvard Medical School, Boston, Massachusetts, USA.
Department of Medicine, Stanford Prevention Research Center, Stanford, California, USA Department of Health Research and Policy, Stanford University School of Medicine, Stanford, California, USA Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, California, USA Meta-Research Innovation Center at Stanford (METRICS), Stanford, California, USA.


Epidemiological studies evaluate multiple exposures, but the extent of multiplicity often remains non-transparent when results are reported. There is extensive debate in the literature on whether multiplicity should be adjusted for in the design, analysis, and reporting of most epidemiological studies, and, if so, how this should be done. The challenges become more acute in an era where the number of exposures that can be studied (the exposome) can be very large. Here, we argue that it can be very insightful to visualize and describe the extent of multiplicity by reporting the number of effective exposures for each category of exposures being assessed, and to describe the distribution of correlation between exposures and/or between exposures and outcomes in epidemiological datasets. The results of new proposed associations can be placed in the context of this background information. An association can be assigned to a percentile of magnitude of effect based on the distribution of effects seen in the field. We offer an example of how such information can be routinely presented in an epidemiological study/dataset using data on 530 exposure and demographic variables classified in 32 categories in the National Health and Nutrition Examination Survey (NHANES). Effects that survive multiplicity considerations and that are large may be prioritized for further scrutiny.


BIOSTATISTICS; Environmental epidemiology; Epidemiological methods; GENETIC EPIDEM

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