1. Department of Biostatistics; Boston University; 801 Massachusetts Avenue Boston 02118 MA U.S.A.
2. Harvard Clinical Research Institute (HCRI); 930 Commonwealth Avenue 3rd floor, Boston 02215 MA U.S.A.
3. Duke Clinical Research Institute (DCRI); Biostatistics and Bioinformatics, Duke University; 2400 Pratt Street Durham 27705 NC U.S.A.
4. Harvard Medical School; Massachusetts General Hospital; 55 Fruit Street, Bulfinch 351 Boston 02114 MA U.S.A.