J. van der Lee, J. Wesseling, M. Tanck, и M. Offringa. Journal of clinical epidemiology, 61 (4):
324-30(апреля 2008)4585<m:linebreak></m:linebreak>PUBM: Print-Electronic; JID: 8801383; RF: 50; 2006/08/29 received; 2007/07/09 revised; 2007/07/12 accepted; 2008/02/21 aheadofprint; ppublish;<m:linebreak></m:linebreak>Tipus d'estudis.