1. Pain Clinic, Department of Anaesthesiology, Intensive Care, Emergency Care and Pain Medicine , Turku University Hospital , P.O. Box 52, FI-20520 , Turku , Finland
2. Department of Nursing Science , University of Turku , FI-20014 , Turku , Finland
3. University of Eastern Finland, School of Educational Sciences and Psychology , P.O. Box 111, FI-80101 , Joensuu , Finland
4. Institute of Behavioural Sciences , P.O. Box 9, FI-00014 , University of Helsinki , Helsinki , Finland