Author contributions
A.P. initiated the study and was responsible for the overall design of the study. B.Ö., P.Z. and H.L. are experts in their respective fields, and critically discussed the study design with A.P. A.P. had the main responsibility. A.P., J.W., Å.D. and H.L. were responsible for data collection. Data analysis was performed by J.W., M.K. and A.P. in dialogue with the university statistician. A.P. and J.W. wrote the manuscript in communication with M.K. All authors read, revised and approved the final version.