Study quality	Diagnosis	Treatment/prevention/screening	Prognosis
Level 1: good-quality, patient-oriented evidence	Validated clinical decision rule	SR/meta-analysis or RCTs with consistent findings	SR/meta-analysis of good-quality cohort studies
	SR/meta-analysis of high-quality studies
		High-quality individual RCT†	Prospective cohort study with good follow-up
	High-quality diagnostic cohort study*
		All-or-none study‡
Level 2: limited-quality patient-oriented evidence	Unvalidated clinical decision rule	SR/meta-analysis of lower quality clinical trials or of studies with inconsistent findings	SR/meta-analysis of lower quality cohort studies or with inconsistent results
	SR/meta-analysis of lower quality studies or studies with inconsistent findings
	Lower quality diagnostic cohort study or diagnostic case-control study	Lower quality clinical trial	Retrospective cohort study or prospective cohort study with poor follow-up
		Cohort study
		Case-control study	Case-control study
			Case series
Level 3: other evidence	Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series for studies of diagnosis, treatment, prevention, or screening