Premium
Comparative effects of the restriction method in two large observational studies of body mass index and mortality among adults
Author(s) -
Flegal Katherine M.,
Graubard Barry I.,
Yi SangWook
Publication year - 2017
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1111/eci.12756
Subject(s) - overweight , underweight , body mass index , observational study , medicine , hazard ratio , obesity , demography , cohort study , sample size determination , cohort , meta analysis , gerontology , confidence interval , statistics , mathematics , sociology
Background A method applied in some large studies of weight and mortality is to begin with a well‐defined analytic cohort and use successive restrictions to control for methodologic bias and arrive at final analytic results. Materials and methods Two observational studies of body mass index and mortality allow a comparative assessment of these restrictions in very large data sets. One was a meta‐analysis of individual participant data with a sample size of 8 million. The second was a study of a South Korean cohort with a sample size of 12 million. Both presented results for participants without pre‐existing disease before and after restricting the sample to never‐smokers and deleting the first 5 years of follow‐up. Results Initial results from both studies were generally similar, with hazard ratios ( HR s) below 1 for overweight and above 1 for underweight and obesity. The meta‐analysis showed higher HR s for overweight and obesity after the restrictions, including a change in the direction of the HR for overweight from 0·99 (95% CI : 0·98–1·01) to 1·11 (95% CI : 1·10, 1·11). The South Korean data showed little effect of the restrictions and the HR for overweight changed from 0·85 (95% CI : 0·84–0·86) to 0·91 (95% CI : 0·90, 0·91). The summary effect size for overweight was 0·90 (95% CI : 0·89–0·91) before restrictions and 1·02 (95% CI : 1·02, 1·03) after restrictions. Conclusions The effect of the restrictions is not consistent across studies, weakening the argument that analyses without such restrictions lack validity.