2,46 Mb - GuíaSalud

Table 2. Levels of evidence and grades of recommendation according to OXFORD
Levels
of evidence
Ia
Ib
II
III
IV
Level 1 studies
Level 2 studies
Level 3 studies
Type of evidence
Systematic review with homogeneity of level 1 studies
Level 1 studies
Level 2 studies
Systematic review of level 2 studies
Level 3 studies
Systematic review of level 3 studies
Consensus, expert opinion without explicit critical appraisal
Follow:
• Blinded comparison to a valid reference test ()
• Appropriate spectrum of patients
• Present only one of these biases:
• Non-representative population (the sample does not refl ect the population group
where the test will be implemented)
• Comparison with an inappropriate reference standard («gold standard») (the
test to be assessed is part of the gold standard or the outcome of the test to be
assessed poses an infl uence on the carrying out of the gold standard
• Non-blinded comparison
• Case control studies
Present two or more criteria in level 2 studies
Recommendation
A
B
C
D
Evidence
Ia or Ib
II
III
IV
124 CLINICAL PRACTICE GUIDELINES IN THE NHS