[1] Univ Iowa, Hosp & Clin, Dept Orthoped & Rehabil, Iowa City, IA 52242 USA
[2] Boston Univ, Sch Med, Boston Univ Clin Epidemiol Res Training Unit, Boston, MA 02118 USA
[3] Univ Iowa, Sch Publ Hlth, Dept Epidemiol, Iowa City, IA 52242 USA
[4] Univ Alabama Birmingham, Div Clin Immunol & Rheumatol, Birmingham, AL 35294 USA
[5] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94107 USA