[1] JOHNS HOPKINS UNIV,DEPT EPIDEMIOL,BALTIMORE,MD 21218
[2] JOHNS HOPKINS UNIV,DEPT HLTH POLICY & MANAGEMENT,BALTIMORE,MD 21218
[3] YESHIVA UNIV ALBERT EINSTEIN COLL MED,DEPT NEUROL,BRONX,NY 10461
[4] GLAXO GRP RES LTD,GREENFORD UB6 0HE,MIDDX,ENGLAND