[1] So Calif Permanente Med Grp, Dept Res & Evaluat, Pasadena, CA 91101 USA
[2] Mayo Clin, Coll Med, Dept Hlth Sci Res, Div Epidemiol, Rochester, MN USA
[3] Mayo Clin, Coll Med, Dept Hlth Sci Res, Div Biostat, Rochester, MN USA
[4] Mayo Clin, Coll Med, Dept Urol, Rochester, MN USA
[5] Merck Res Labs, Dept Epidemiol, Blue Bell, PA USA