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Journal of Obesity
Volume 2010 (2010), Article ID 413407, 3 pages
http://dx.doi.org/10.1155/2010/413407
Research Article

Measurement of Weight in Clinical Trials: Is One Day Enough?

1Division of General Internal Medicine, The Johns Hopkins University School of Medicine, 2024 E Monument, Room 2-518, Baltimore, MD 21287, USA
2Center for Health Research, Kaiser Permanente, Portland, OR 97227, USA
3Welch Center for Prevention, Epidemiology, and Clinical Research, The Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA
4Department of Epidemiology, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21287, USA
5Department of Kinesiology, Towson University, Towson, MD 21252, USA
6Division of Endocrinology, Metabolism, and Nutrition, Duke University Medical Center, Durham, NC 27710, USA
7National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20824, USA

Received 27 May 2010; Accepted 9 July 2010

Academic Editor: Jack Adam Yanovski

Copyright © 2010 Nisa M. Maruthur et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background. Weight is typically measured on a single day in research studies. This practice assumes negligible day-to-day weight variability, although little evidence exists to support this assumption. We compared the precision of measuring weight on one versus two days among control participants in the Weight Loss Maintenance trial. Methods. Trained staff measured weight on two separate days at baseline, 12 months, and 30 months (2004–2007). We calculated the standard deviation (SD) of mean weight change from baseline to the 12- and 30-month visits using (a) the first and (b) both daily weights from each visit and conducted a variance components analysis (2009). Results. Of the 316 participants with follow-up measurements, mean (SD) age was 55.8 (8.5) years, BMI was 30.8 (4.5) kg/ , 64% were women, 36% were black, and 50% were obese. At 12 months, the SD of mean weight change was 5.1 versus 5.0 kg using one versus two days of weight measurements , while at 30 months the corresponding SDs were 6.3 and 6.3 kg . We observed similar findings within subgroups of BMI, sex, and race. Day-to-day variability within individuals accounted for <1% of variability in weight. Conclusions. Measurement of weight on two separate days has no advantage over measurement on a single day in studies with well-standardized weight measurement protocols.