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Systematic reviews: Level of evidence

Level of evidence

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.

Level of evidence

 ‘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
recommandation

Level of evidence

Type of study

A

1a

  Systematic review of (homogeneous) 
  radomized controlled trials

1b

  Individual randomized controlled trials (with    narrow confidence intervals)

B

2a

  Systematic review of (homogenous) cohort   
  studies of ”exposed” and ”unexposed” subjects

2b

  Individual cohort study / low-quality 
  randomized  controlled trials

3a

  Systematic review of (homogenous) case-
  control studies

3b

  Individual case-control studies

C

4

  Case-series, low quality cohort studies or
  case-control studies

D

5

  Expert opinions based on non systematic 
  reviews of results or mechanistic studies

John Hopkins

Johns Hopkins Nursing EBP: Levels of Evidence

  • Level I. Experimental study, randomized controlled trial (RCT) ...
  • Level II. Quasi-experimental Study. ...
  • Level III. Non-experimental study. ...
  • Level IV. Opinion of respected authorities and/or nationally recognized expert committees/consensus panels based on scientific evidence. ...
  • Level V.