[1] Int Agcy Res Canc, Unit Field & Intervent Studies, F-69372 Lyon 08, France
[2] Karolinska Inst, Dept Med Epidemiol, Stockholm, Sweden
[3] Harvard Univ, Sch Publ Hlth, Dept Epidemiol, Boston, MA 02115 USA
[4] Soder Sjukhuset, Dept Clin Epidemiol, S-10064 Stockholm, Sweden