A |
1A |
Systematic review (with homogeneity) of randomized controlled clinical trials |
Systematic review (with homogeneity) of cohorts since disease onset Prognostic criteria validated in different populations |
Systematic review (with homogeneity) of level 1 diagnostic studies Diagnostic criteria of level 1B studies conducted at different clinical centers |
Systematic review (with homogeneity) of cohort study (contemporary or prospective) |
1B |
Randomized controlled clinical trials with narrow confidence interval |
Cohort, since disease onset, with losses < 20% Prognostic criteria validated in a single population |
Validity cohort, with good reference standard Diagnostic criteria tested at a single clinical center |
Cohort study (contemporary or prospective) with few losses |
1C |
“All or none” treatment results |
“All or none” case-series |
Sensitivity and specificity close to 100% |
“All or none” case-series |
B |
2A |
Systematic review (with homogeneity) of cohort studies |
Systematic review (with homogeneity) of historical cohorts (retrospective) or of follow-up of untreated control patients in a randomized clinical trial |
Systematic review (with homogeneity) of level >2 diagnostic studies |
Systematic review (with homogeneity) of level ≥ 2B differential diagnosis studies |
2B |
Cohort study (including randomized clinical trial of lower quality) |
Historical cohort study Follow-up of untreated control patients in a randomized clinical trial Prognostic criteria derived from or validated on split samples only |
Exploratory cohort study with good reference standard Diagnostic criteria derived from or validated on split samples or database |
Historical cohort study (retrospective cohort) or with poor follow-up of cases (large number of losses) |
2C |
Observation of treatment results (outcomes research) Ecological Study |
Observation of clinical progression (outcomes research) |
|
Ecological study |
3A |
Systematic review (with homogeneity) case-control studies |
|
Systematic review (with homogeneity) of level ≥ 3B diagnostic studies |
Systematic review (with homogeneity) of level ≥ 3B studies |
3B |
Case-control study |
|
Non-consecutive case selection, or inconsistently applied reference standard |
Cohort with non-consecutive case selection, or very limited study population |
C |
4 |
Case reports (including poor quality cohort or case-control studies) |
Case-series (and poor quality prognostic cohort studies) |
Case-control study or poor or non-independent reference standard |
Case-series, or superseded reference standard |
D |
5 |
Expert opinion without critical appraisal or based on basic materials (physiological study or study with animals) |