A—High Quality

consistent, generalizable results; sufficient sample size for the study design, adequate control; definitive conclusions; consistent recommendations based on comprehensive literature review that includes thorough reference to scientific evidence

B—Good Quality

reasonably consistent results; sufficient sample size for the study design; some control; fairly definitive conclusions; reasonably consistent recommendations based on fairly comprehensive literature review that includes some references to scientific evidence

C—Low Quality

little evidence with inconsistent results; insufficient sample size for the study design; conclusions cannot be drawn