1. Helsinki University Central Hospital, P.O. Box 340, 00029 HUS, Finland
2. Department of Nursing Science and Turku University Hospital, Turku University, 20004 Turku, Finland
3. Department of Biostatistics, Turku University, 20004 Turku, Finland
4. Helsinki University Central Hospital, P.O. Box 280, 00029 HUS, Finland