[1] Univ Vermont, Coll Med, Dept Pathol, Burlington, VT 05405 USA
[2] Univ Washington, Dept Biostat, Seattle, WA 98195 USA
[3] Univ Pittsburgh, Sch Publ Hlth, Dept Epidemiol, Pittsburgh, PA 15260 USA
[4] NHLBI, Div Epidemiol & Clin Applicat, NIH, Bethesda, MD 20892 USA
[5] Johns Hopkins Univ, Sch Publ Hlth Epidemiol, Baltimore, MD USA
[6] Univ Vermont, Dept Biochem, Burlington, VT 05405 USA