Level of Evidence

Topic updated on 03/16/14 8:42pm
  • A method utilized in evidenced based medicine to determine the clinical value of a study
  • See details of Clinical Design Trials 
Different Levels of Evidence
Level 1
  1. Randomized controlled trial (RCT)
    • a study in which patients are randomly assigned to the treatment or control group and are followed prospectively
  2. Meta-analysis of randomized trials with homogeneous results
Level 2  
  1. Prospective comparative study (therapeutic) 
    • a study in which patient groups are separated non-randomly by exposure or treatment, with exposure occurring after the initiation of the study
  2. Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results 
Level 3
  1. Retrospective cohort study
    • a study in which patient groups are separated non-randomly by exposure or treatment, with exposure occurring before the initiation of the study
  2. Case-control study
    • a study in which patient groups are separated by the current presence or absence of disease and examined for the prior exposure of interest
  3. Meta-analysis of Level 3 studies 
Level 4
  1. Case series
    • a report of multiple patients with the same treatment, but no control group or comparison group
Level 5
  1. Case report (a report of a single case)
  2. Expert opinion
  3. Personal observation



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Qbank (6 Questions)

(OBQ12.100) A therapeutic study presents a systematic review of 15 high-quality randomized controlled trials with homogeneous results. What level of evidence is this considered? Topic Review Topic

1. I
2. II
3. III
4. IV
5. V

(OBQ12.188) An orthopaedic resident wants to answer a focused research question of whether mobile bearing knee arthroplasty has superior functional outcomes compared to fixed bearing knee arthroplasty. The resident mathematically combines the results from multiple retrospective cohort studies following QUORUM (Quality of Reporting of Meta-analyses) guidelines. What is the highest level of evidence that this meta-analysis can achieve? Topic Review Topic

1. Level I
2. Level II
3. Level III
4. Level IV
5. Level V

(OBQ11.239) In the study by Moseley et al published in the New England Journal of Medicine, 180 patients with knee osteoarthritis were randomly assigned via sealed envelope to receive arthroscopic débridement, arthroscopic lavage, or placebo surgery. Outcomes were assessed by blinded evaluators at several points over a 2 year period with the use of five self-reported pain and function scores. There was a greater than 90% follow-up in the study. This study is best described as having which level of evidence? Topic Review Topic

1. Therapeutic study, evidence level I
2. Therapeutic study, evidence level II
3. Diagnostic study, evidence level I
4. Diagnostic study, evidence level II
5. Prognostic study, evidence level I

(OBQ10.242) Which of the following study designs represent a level III evidence study? Topic Review Topic

1. Prospective, randomized controlled trial
2. Retrospective case-control study
3. Retrospective case series
4. Prospective cohort study
5. Expert opinion

(OBQ08.127) Using levels of evidence in research studies, which of the following represents a level II study? Topic Review Topic

1. Retrospective case control study
2. Prospective cohort study
3. Case report of 3 patients with the same disease
4. High-quality randomized prospective clinical trial
5. The opinion of a review panel at the annual AAOS meeting



Wright RW, Brand RA, Dunn W, Spindler KP
Clin. Orthop. Relat. Res.. 2007 Feb;455:23-9. PMID: 17279036 (Link to Pubmed)
17 responses
Bhandari M, Morrow F, Kulkarni AV, Tornetta P
J Bone Joint Surg Am. 2001 Jan;83-A(1):15-24. PMID: 11205853 (Link to Pubmed)
21 responses
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