1. Department of Preventive Medicine; Northwestern University; Chicago, Illinois 60611 U.S.A.
2. Division of Cardiovascular Medicine, Brigham & Women's Hospital; Harvard Medical School; Boston, Massachusetts 02115 U.S.A.
3. Department of Health Research and Policy; Stanford University; Stanford, California 94305 U.S.A.
4. Department of Medical Oncology; Dana-Farber Cancer Institute; Boston, Massachusetts 02115 U.S.A.
5. Department of Biostatistics and Computational Biology; Dana-Farber Cancer Institute; Boston, Massachusetts 02115 U.S.A.
6. Department of Biostatistics; Harvard University; Boston, Massachusetts 02115 U.S.A.