1. Department of Mathematical Statistics, Stockholm University, S‐106 91 Stockholm.
2. Department of Medical Epidemiology, Karolinska Institute, S‐171 77 Stockholm, Sweden.
3. Department of Radiobiology, Stockholm University, S‐106 91 Stockholm, Sweden.
4. AkZO Nobel, Casco Products AB, P.O. Box 11538, Stockholm, Sweden.
5. Department of Environmental Chemistry, Stockholm University, S‐106 91 Stockholm, Sweden.