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Ranking of evidence by study type

Ranking of evidence by study type
T1 Randomised controlled trial (RCT)
T2 Controlled trial (CT)
T3 Controlled before-and-after intervention study (CBA)
O1 Cohort study / longitudinal study
O2 Case-control study
O3 Cross-sectional
O4 Study using qualitative methods only
O5 Case series
O6 Case study
X Formal consensus or other professional (expert) opinion (automatic exclusion)

 

Definition of levels of evidence and grading practice recommendations 1
Grade Level Type of evidence
A Ia Evidence obtained from a well designed randomised controlled trial of appropriate size (T1)
B Ib Evidence obtained from a well designed controlled trial without randomisation (T2, T3)
B IIa Evidence obtained from a well designed controlled observational study e.g. cohort, case-control or cross-sectional studies. (Also include studies using purely qualitative methods) (O1, O2)
C IIb Evidence obtained from a well designed uncontrolled observational study (O3, O4)
C III Evidence obtained from studies that are case series or case studies (O5, O6)

 

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