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:
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
>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.
>Roger Keller Celeste
>Doutorando Epidemiologia (PhD student)
>Instituto de Medicina Social - UERJ
>Rua São Francisco Xavier, 524 7o ANDAR
>Rio de Janeiro - Brasil
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Department of Primary Health Care &
Director, Centre for Evidence-Based Practice, Oxford