[1] Univ Oulu, Inst Biomed, Oulu, Finland
[2] Univ Oulu, Bioctr Oulu, Oulu, Finland
[3] Univ Oulu, Dept Anat, Oulu, Finland
[4] Univ Oulu, Dept Surg, Oulu, Finland
[5] Inst Hlth Sci, Oulu, Finland
[6] Imperial Coll London, Dept Epidemiol & Biostat, London, England