Obesity and Diabetes Clinical Research Section, Phoenix Epidemiology and Clinical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 4212 North 16th Street, Room 541, Phoenix, AZ, 85016, USA. Department of Epidemiology & Biostatistics, Drexel University, Philadelphia, PA, USA. Arizona State University, Tempe, AZ, USA. Obesity and Diabetes Clinical Research Section, Phoenix Epidemiology and Clinical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 4212 North 16th Street, Room 541, Phoenix, AZ, 85016, USA. gmarci@niddk.nih.gov.