Evidence for claims

Grading and quality of clinical scientific evidence

Thanks to Andy Gray for bringing this to my attention.

The WHO Handbook for Guideline Development explains the process: 

"Quality is defined as the ʹextent to which one can be confident that an estimate of effect or association is correctʹ. It is a continuum, as any discrete categorization involves some degree of arbitrariness. It is based on the following criteria:

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