To the Editor: The study by Dr Flegal and colleagues1 showed that those persons in the overweight category (BMI 25 to <30) had a lower number of excess deaths compared with those in the normal-weight category (BMI 18.5 to <25). However, their summary results were obtained from pooling 3 separate cohorts of statistically divergent results from very heterogeneous time periods, a factor that has major methodological implications in how these data should be statistically pooled.
The cohort-specific estimates were based on the populations of NHANES I, II, and III, ranging from 1971 to 1994. Due to heterogeneity of available medical treatments over more than 20 years, the implications of long-term survival from being overweight and obese may be different across the different decades. This heterogeneity suggests that the proper method of pooling the differential estimates into a summary statistic is a random-effects model.2 - 3 Although the analysis included standardization of smoking, alcohol consumption, and demographic characteristics, the heterogeneous rates of disease screening, new surgical techniques, and use of new medical treatments across 2 decades were not adjusted for in their analysis. It would therefore be interesting to know if statistical heterogeneity existed in the excess mortality and relative risk estimates in the different cohorts and if the statistical significance of the pooled confidence intervals is retained in random-effects models.
Financial Disclosures: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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