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"Scientists believe in proof without certainty; most people believe in certainty without proof." (Ashely Montagu; from http://meds.queensu.ca/medicine/obgyn/links/criteria_for_causation.htm )
It has been proposed that the Grading of Recommendations Assessment, Development and Evaluation (GRADE) for public health questions should consider the Bradford Hill criteria for causation and that GRADE requires adaptation. 1 In this article, we describe the relation of the Bradford Hill criteria to the GRADE approach to grading the quality of evidence and strength of recommendations. The primary concern seems that evidence from non-randomised studies may provide a more adequate or best available measure of a public health strategy's impact, but that such evidence might be graded as lower quality in the GRADE framework. We would like to reiterate that GRADE presents a framework that describes both criteria for assessing the quality of research evidence and the strength of recommendations. In assessing quality of evidence, GRADE notes that randomisation is only one of many relevant factors. Furthermore, GRADE is not specific to the narrow field of therapeutic interventions. Indeed, it likely is the most broadly applied framework for evaluation of evidence and developing recommendations.
We would like to clarify several issues that have been raised in a recent editorial published in the Journal of Epidemiology and Community Health. 1 First, concern has been expressed that herd immunity as a result of immunisation and indirect effects on the co-circulation of other pathogens are typically ascertained through the use of observational epidemiological methods. Although we do not disagree with this assessment, we would like to point out that, innovative randomised controlled trials (RCTs) using cluster-randomisation can be conducted to provide such information. 2 Second, concern is expressed that a quasi-RCT that found a 94% protective effect of a live, monovalent vaccine against measles was classified as 'moderate level of scientific evidence'. However, GRADE's strength of association criteria can be applied to quasi-RCTS and observational studies with no major threats to validity to upgrade the quality of evidence (see below). Such a judgement would be possible in this situation. Third, it is implied that GRADE ratings do not give credit to the 'gradient of effects with scale of population level impact compatible with degree of coverage'. However, we would like to clarify that GRADE's dose-response criterion is not...