[1] Northwestern Univ, Feinberg Sch Med, Dept Prevent Med, Chicago, IL 60611 USA
[2] Johns Hopkins Univ, Dept Med, Baltimore, MD USA
[3] Univ Minnesota, Div Epidemiol & Community Hlth, Minneapolis, MN USA
[4] Amer Canc Soc, Epidemiol Res Program, Atlanta, GA 30329 USA