Paul G Shekelle1, Ian A Cook2, Selene Mak3. 1. West Los Angeles Veterans Affairs Medical Center, Los Angeles, California (P.G.S.). 2. West Los Angeles Veterans Affairs Medical Center and David Geffen School of Medicine and Henry Samueli School of Engineering and Applied Science at University of California, Los Angeles, Los Angeles, California (I.A.C.). 3. West Los Angeles Veterans Affairs Medical Center and Fielding School of Public Health at University of California, Los Angeles, Los Angeles, California (S.M.).