1. Department of Biostatistics, University of Oslo , Oslo , Norway
2. Department of Mathematics, EPFL , Lausanne , Switzerland
3. Department of Research, Cancer Registry of Norway, Norwegian Institute of Public Health , Oslo , Norway
4. Department of Mathematics and Computer Science, University of Bremen , Bremen , Germany
5. Leibniz Institute for Prevention Research and Epidemiology – BIPS , Achterstr 30, D-28359 Bremen , Germany