Burns PB, Rohrich RJ, Chung KC. The levels of evidence and their role in evidence-based medicine. Plast Reconstr Surg. 2011 Jul;128(1):305-310. doi: 10.1097/PRS.0b013e318219c171. PMID: 21701348; PMCID: PMC3124652.
‘Levels of evidence’ specify a hierarchical order for various research designs based on their internal validity. A grade 1A.evidence means the evidence in a SR is a synthesis of randomised controlled trials (RTCs).
|
Grade of |
Level of evidence |
Type of study |
|
A |
1a |
Systematic review of (homogeneous) |
|
1b |
Individual randomized controlled trials (with narrow confidence intervals) |
|
|
B |
2a |
Systematic review of (homogenous) cohort |
|
2b |
Individual cohort study / low-quality |
|
|
3a |
Systematic review of (homogenous) case- |
|
|
3b |
Individual case-control studies |
|
|
C |
4 |
Case-series, low quality cohort studies or |
|
D |
5 |
Expert opinions based on non systematic |
Johns Hopkins Nursing EBP: Levels of Evidence