Study of Osteoporotic Fractures Research Group Members:San Francisco Coordinating Center (California Pacific Medical Center Research Institute and University of California San Francisco): Steven R. Cummings, MD (principal investigator), Michael C. Nevitt, PhD, MPH (coinvestigator), Douglas C. Bauer, MD (coinvestigator), Dennis M. Black, PhD (coinvestigator), Katie L. Stone, PhD (coinvestigator), Warren S. Browner, MD, MPH (coinvestigator), R. Benard, T. Blackwell, P. M. Cawthon, L. Concepcion, M. Dockrell, S. Ewing, M. Farrell, C. Fox, R. Fullman, S. L. Harrison, M. Jaime-Chavez, D. Kriesel, W. Liu, Li-Yung Lui, MA, MS, L. Palermo, N. Parimi, M. Rahorst, C. Schambach, R. Scott, and J. Ziarno. University of Maryland: Marc C. Hochberg, MD, MPH (principal investigator), R. Nichols (clinic coordinator), S. Link. University of Minnesota: Kristine E. Ensrud, MD, MPH (principal investigator), Susan J. Diem, MD, MPH (coinvestigator), Mary C. Homan, MD, MPH (coinvestigator), P. Van Coevering (program coordinator), S. Fillhouer (clinic director), N. Nelson (clinic coordinator), K. Moen (assistant program coordinator), R. Andrews, K. Atchison, C. Bowie, M. Forseth, R. Gran, F. Imker-Witte, K. Jacobson, S. Luthi, N. Muehlbauer, and M. Slindee. University of Pittsburgh, Pittsburgh, Pennsylvania: Jane A. Cauley, DrPH (principal investigator), Lewis H. Kuller, MD, DrPH (co–principal investigator), Joseph M. Zmuda, PhD (coinvestigator), L. Harper (project director), L. Buck (clinic coordinator), M. Danielson (project administrator), C. Bashada, D. Cusick, A. Flaugh, M. Gorecki, M. Nasim, C. Newman, and N. Watson. The Kaiser Permanente Center for Health Research, Portland, Oregon: Teresa A. Hillier, MD, MS (principal investigator), Kimberly K. Vesco, MD, MPH (coinvestigator), Kathryn L. Pedula, MS (coinvestigator), J. Van Marter (project director), M. Summer (clinic coordinator), A. MacFarlane, J. Rizzo, K. Snider, and J. Wallace.