[1] Department of Clinical Epidemiology and Biostatistics,
[2] Academic Medical Centre,undefined
[3] University of Amsterdam,undefined
[4] PO Box 22700,undefined
[5] 1100 DE Amsterdam,undefined
[6] The Netherlands e-mail: craen@lumc.nl,undefined
[7] Tel.: +31-20-5665602,undefined
[8] Fax: +31-20-6912683,undefined
[9] Department of Neurology,undefined
[10] Academic Medical Centre,undefined
[11] University of Amsterdam,undefined
[12] PO Box 22700,undefined
[13] 1100 DE Amsterdam,undefined
[14] The Netherlands,undefined
[15] NHS Centre for Reviews and Dissemination,undefined
[16] University of York,undefined
[17] York,undefined
[18] YO1 5DD,undefined
[19] UK,undefined