The 6S Pyramid (DiCenso, Bayley, & Haynes, 2009).
Critically-appraised individual articles and synopses include:
Filtered evidence:
Unfiltered evidence:
Two things to remember:
1. Studies in which randomization occurs represent a higher level of evidence than those in which subject selection is not random.
2. Controlled studies carry a higher level of evidence than those in which control groups are not used.
Grade of Recommendation |
Level of Evidence |
Type of Study |
A | 1a | Systematic review of (homogeneous) randomized controlled trials |
A | 1b | Individual randomized controlled trials (with narrow confidence intervals) |
B | 2a | Systematic review of (homogeneous) cohort studies of "exposed" and "unexposed" subjects |
B | 2b | Individual cohort study / low-quality randomized control studies |
B | 3a | Systematic review of (homogeneous) case-control studies |
B | 3b | Individual case-control studies |
C | 4 | Case series, low-quality cohort or case-control studies |
D | 5 | Expert opinions based on non-systematic reviews of results or mechanistic studies |