By vgreene, 24 December, 2014 X:Exceptional situations where validating studies cannot be performed and there is clear preponderance of benefit or harm
By vgreene, 24 December, 2014 C:Single or few observational studies or multiple studies w/ inconsistent findings/major limitations
By vgreene, 24 December, 2014 B:Trials/diagnostic studies w/ minor limitations; consistent findings from multiple observational studies
By vgreene, 24 December, 2014 A:Intervention—well-designed trials, meta-analyses; Diagnosis—independent gold standard studies