aInstitute for Research in Extramural Medicine, Faculty of Medicine, Vrije Universiteit, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands
bInstitute for Rehabilitation Sciences, P.O. 192, 6430 AD, Hoensbroek, The Netherlands
cPain Management and Research Centre, University Hospital Maastricht, P.O. 5800, 6202 AZ, Maastricht, The Netherlands
dDepartment of Epidemiology, Faculty of Health Sciences, Maastricht University, P.O. 616, 6200 MD, Maastricht, The Netherlands
* Corresponding author. Tel.: +31-20-444-8354; fax: +31-20-444-8181; e-mail: [email protected]
Received May 28, 1998; received in revised form January 7, 1999; accepted January 11, 1999