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Definition of levels of evidence and grading practice recommendations

Practice recommendations1,2

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 study or case series (O5, O6)

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References

  1. This classification is based on the Bandolier system adapted to include theĀ  Centre for Reviews and Dissemination. Systematic Reviews: CRD's Guidance for Undertaking Reviews in Health Care, 2009 Centre for Reviews and Dissemination, University of York. [PDF from York University]
  2. Weaver N, Williams JL, Weightman AL, Kitcher HN, Temple JM, Jones P, Palmer S. Taking STOX: developing a cross disciplinary methodology for systematic reviews of research on the built environment and the health of the public. Journal of Epidemiology and Community Health. 2002;56(1):48-55. [Pubmed]

 

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