Dear Roger, You raise a good point. Ecological studies suffer from both ecological fallacy (which is a form of confounding) and from misclassification biases, which I'd expect are at least as great as for case-control studies. So perhaps a 3c rating would be more appropriate. The GRADE working group is working hard to come up with a better system: http://www.gradeworkinggroup.org/ Cheers Paul Glasziou At 26/03/2006, Roger Keller Celeste wrote: >Hi dear list, >I would like some help from you. I may be misinterpreting some concepts. > >Looking closer to the table of levels of >evidence in >http://www.cebm.net/levels_of_evidence.asp, I >noticed that ecological studies are rated better >than systematic reviews (with homogeneity) of case-control studies. > >It may be ignorance of me, but what happened to >the ecological fallacy? Aren't the >etiology/therapy studies concerned with >individual inferences? Aren't case-control >studies more likely to establish temporal relationships? > >Finally, where should I put good cross-sectional >studies? In some fields, they are the only evidence available. > >Thanks >Roger Keller Celeste >Doutorando Epidemiologia (PhD student) >Instituto de Medicina Social - UERJ >Rua São Francisco Xavier, 524 7o ANDAR >Rio de Janeiro - Brasil > > > > >_______________________________________________________ >Novo Yahoo! Messenger com voz: Instale agora e >faça ligações de graça. http://br.messenger.yahoo.com/ Paul Glasziou Department of Primary Health Care & Director, Centre for Evidence-Based Practice, Oxford ph: 44-1865-227055