Published by Oxford University Press on behalf of the International Epidemiological Association © The Author 2008; all rights reserved.
Commentary: Flawed study designs are not salvaged by large samples
Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
E-mail: walter.willett@channing.harvard.edu
Accepted 29 July 2008
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In this issue, Bingham et al.1 present analyses comparing nutrient intakes estimated by a 1-week diet record (DR) or food frequency questionnaire (FFQ) to a series of biomarkers and incidence of coronary heart disease (CHD). Such triangulation analyses can provide valuable evidence on the relative validity of different dietary assessment methods and are thus of considerable interest. Unfortunately, the results provided by Bingham et al. are difficult to interpret due to the design of the study and their choice of statistical models.
In the design of a study in which multiple dietary assessment methods are compared with biomarkers, the temporal relationships are critical. Underlying this is the concept that, for epidemiologic applications, the dietary methods are meant to represent intake over an extended period, usually many months or years, not just the few days or weeks around the time the data are collected. Thus, if the biomarker is sensitive to
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