G. Fransen, C. van Marrewijk, S. Mujakovic, J. Muris, R. Laheij, M. Numans, N. de Wit, M. Samsom, J. Jansen, and J. Knottnerus. BMC medical research methodology, (January 2007)4304<m:linebreak></m:linebreak>LR: 20071115; PUBM: Electronic; DEP: 20070423; JID: 100968545; 0 (Histamine H2 Antagonists); 0 (Proton Pumps); RF: 24; 2007/02/14 received; 2007/04/23 accepted; 2007/04/23 aheadofprint; epublish;<m:linebreak></m:linebreak>Tipus d'estudis.