[1] Washington Univ, Sch Med, St Louis, MO 63110 USA
[2] Washington Univ, Sch Med, Div Biostat, St Louis, MO 63110 USA
[3] Washington Univ, Sch Med, Dept Orthopaed Surg, Div Phys Med & Rehabil, Box MSC 8233-0004-05,660S S Euclid Ave, St Louis, MO 63110 USA
[4] Univ Washington, Dept Psychiat & Behav Sci, Seattle, WA 98195 USA