1. Department of Epidemiology and Biostatistics; Memorial Sloan Kettering Cancer Center; New York 10017 U.S.A.
2. Departments of Family Medicine and Biostatistics; University of Michigan; Ann Arbor, Michigan 48104 U.S.A.
3. Division of Cancer Epidemiology and Genetics; National Cancer Insitute; Rockville, Maryland 20892 U.S.A.
4. Cancer Registry of Norway; Institute of Population-Based Cancer Research; Oslo 0304 Norway
5. Department of Epidemiology; University of North Carolina; Chapel Hill, North Carolina 27599 U.S.A.