Combining Risk Estimates from Observational Studies with Different Exposure Cutpoints: A Meta-analysis on Body Mass Index and Diabetes Type 2

• Published in: American journal of epidemiology Vol. 163; no. 11; pp. 1042 - 1052
• Main Authors: Hartemink, Nienke, Boshuizen, Hendriek C., Nagelkerke, Nico J. D., Jacobs, Monique A. M., van Houwelingen, Hans C.
• Format: Journal Article
• Language: English
• Published: Cary, NC Oxford University Press 01-06-2006; Oxford Publishing Limited (England)
• Subjects: Analysis. Health state; Biological and medical sciences; Body Mass Index; Data Interpretation, Statistical; Diabetes; diabetes mellitus; Diabetes Mellitus, Type 2 - epidemiology; Diabetes. Impaired glucose tolerance; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Epidemiology; Etiopathogenesis. Screening. Investigations. Target tissue resistance; General aspects; Humans; Medical sciences; Meta-analysis; Metabolic diseases; Obesity; Public health. Hygiene; Public health. Hygiene-occupational medicine; Risk Assessment; Risk Factors; Endocrinopathy; Type 2 diabetes; Human; Obesity; Observational study; Estimation; Nutrition disorder; meta-analysis; Metabolic diseases; Exposure; diabetes mellitus; Review; Epidemiology; Metaanalysis; Body mass index; Risk factor; Nutritional status
• ISSN: 0002-9262; 1476-6256
• DOI: 10.1093/aje/kwj141

Studies on a dose-response relation often report separate relative risks for several risk classes compared with a referent class. When performing a meta-analysis of such studies, one has to convert these relative risks into an overall relative risk for a continuous effect. Apart from taking the dependence between separate relative risks into account, this implies assigning an exposure level to each risk factor class and allowing for the nonlinearity of the dose-response relation. The authors describe a relatively simple method solving these problems. As an illustration, they applied this method in a meta-analysis of the association between body mass index and diabetes type 2, restricted to results of follow-up studies (n = 31). Results were compared with a more ad hoc method of assigning exposure levels and with a method in which the nonlinearity of the dose-response method was not taken into account. Differences with the ad hoc method were larger in studies with fewer categories. Not incorporating the nonlinearity of the dose response leads to an overestimation of the pooled relative risk, but this bias is relatively small.