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Introduction
  • 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
 
 JBJS LOE
AAOS Recommendations
 

AAOS Evidence-Based Practice Committee

  Recommendations in Clinical Practice Guidelines

Strong • Two or more HIGH quality studies
Moderate  • One HIGH or 2 MODERATE quality studies
Weak 

• One MODERATE or 1 or more LOW quality studies

Consensus
• Expert opinion (no studies)* Only used in one circumstance: It pertains to medical interventions that potentially prevent loss of life or limb (catastrophic consequences).

 
 
 

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Questions (6)

(OBQ13.33) A physician is interested in using platelet-rich plasma (PRP) for treatment of osteochondral lesions of the talus. He is reviewing a prospective cohort study that compares 40 patients treated with PRP and cast immobilization for 6 weeks vs. 36 patients treated conservatively with cast immobilization for 6 weeks. All patients were treated at the same time and institution. The study was not randomized although treatment and control groups were matched appropriately to reduce selection bias. Follow-up in each group was >80% over 1 year. The paper reported significant improvement with use of PRP based on three standard foot and ankle outcome scores (AOFAS, SF-36, FOAS). What is the level of evidence for this study? Review Topic

QID:4668
1

Level I

2%

(44/2032)

2

Level II

72%

(1456/2032)

3

Level III

23%

(458/2032)

4

Level IV

3%

(54/2032)

5

Level V

0%

(3/2032)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

This is prospective cohort study with Level-II evidence.

Level of evidence provides guidance to the study quality. It is used to assess therapeutic studies (as with this question), prognostic studies, diagnostic studies and economic or decision models. When determining the level of evidence, readers must critically appraise the study question, treatment, intervention and outcomes of the study design. Level-II therapeutic studies consist of well-designed prospective cohort studies, poor-quality randomized controlled trials (follow-up less than 80%) and systematic review of Level-II studies or non-homogenous Level-I studies.

Wright et al. provided an excellent summary of clinical research study level of evidence. This has been provided as Illustration A.

Illustration A shows a chart of level of evidence. There is a column for each type of study which corresponds to a row that outlines the level of evidence based on study design.

Incorrect Answers:
Answer 1: Level-I evidence include randomized controlled studies with follow-up>80% and systematic review of Level-I RTC studies (homogenous studies)
Answer 3: Level-III evidence include case control studies, retrospective cohort studies and systematic review of Level-III studies
Answer 4: Level-IV evidence include case series with no control group (or compare to a historical control group)
Answer 5: Level V evidence include expert opinion

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(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? Review Topic

QID:4460
1

I

71%

(2109/2963)

2

II

14%

(410/2963)

3

III

8%

(245/2963)

4

IV

4%

(130/2963)

5

V

2%

(45/2963)

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

A systematic review of high-quality clinical trials is considered a Level I study.

A systematic review is a powerful tool used to identify, evaluate and appraise all high-quality research related to a specific question. Systematic reviews, in contrast to most narrative review articles, adhere to strict scientific design by following eight steps; 1) defining a question and developing inclusion criteria, 2) searching for studies, 3) selecting studies and collecting data, 4) assessing risk of bias, 5) data analysis and meta-analyses, 6) addressing biases, 7) presenting results, and 8) interpreting results and drawing conclusions. When the results from the systematic review are homogeneous (less variability between studies than would be expected by chance), the data from a systematic review can be combined into a meta-analysis.

Wright et al. discuss the levels of evidence in orthopaedic journals as presented by the AAOS Evidence-Based Practice Committee. Based on levels of evidence, the AAOS provides grades of recommendation (A, B, C, I). Grade A recommendations are supported by Level 1 studies with consistent findings, whereas Grade I do not have enough evidence to support a recommendation.

Illustration A shows an "evidence pyramid." MA = meta-analysis, SR = systematic review, RCT = randomized controlled trial.

Incorrect Answers:
Answer 2: An example of a Level II study is prospective comparative study.
Answer 3: An example of a Level III study is a case control trial.
Answer 4: An example of a Level IV study is a case series.
Answer 5: An example of a Level V study is one based on expert opinion.

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(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? Review Topic

QID:4548
1

Level I

8%

(271/3408)

2

Level II

23%

(782/3408)

3

Level III

57%

(1954/3408)

4

Level IV

10%

(346/3408)

5

Level V

1%

(28/3408)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

The level of evidence assigned to a meta-analysis is based on the lowest level of evidence of the included studies. In this case, the studies included in the meta-analysis were retrospective cohort (Level III) studies.

A meta-analysis is a systematic review that combines the results of multiple studies to answer a focused clinical question.

Clarke discusses the QUORUM guidelines which are intended to address standards for improving the quality of reporting of meta-analyses of clinical randomized controlled trials. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement and MOOSE (Meta-analysis Of Observational Studies in Epidemiology) guidelines are similar standards. A similar set of guidelines called CONSORT (Consolidated Standards of Reporting Trials) guidelines are available for randomized trials.

Incorrect Answers:
1: Level I studies include high-quality randomized controlled trials
2: Level II studies include lower-quality RCTs and prospective cohort studies.
4: Level IV studies include case-series or poor-quality cohort and case-control studies.
5: Level V studes are expert opinion articles.


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(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 d├ębridement, 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? Review Topic

QID:3662
1

Therapeutic study, evidence level I

86%

(262/305)

2

Therapeutic study, evidence level II

6%

(19/305)

3

Diagnostic study, evidence level I

2%

(7/305)

4

Diagnostic study, evidence level II

0%

(0/305)

5

Prognostic study, evidence level I

5%

(16/305)

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

Therapeutic studies investigate the results of treatment. Level 1 evidence includes randomized controlled trial with statistically significant difference or no statistically significant difference but narrow confidence interval

A level II therapeutic study would include a lesser-quality randomized controlled trial (eg, <80% follow-up, no blinding, or improper randomization). A non-randomized prospective cohort study that compares the results of treatment or systematic reviews of level II studies or level I studies with heterogenous results would also be considered a level II study.

Prognostic studies investigate the effect of a patient characteristic on the outcome of disease. Diagnostic studies investigate the efficacy of a diagnostic test. Illustration A is a table detailing the levels of evidence.

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

QID:3341
1

Prospective, randomized controlled trial

1%

(13/1352)

2

Retrospective case-control study

74%

(1006/1352)

3

Retrospective case series

16%

(222/1352)

4

Prospective cohort study

7%

(91/1352)

5

Expert opinion

1%

(15/1352)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

The practice of evidence based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research. Therapeutic study hierarchy of evidence has been established to better analyze studies in a reproducible fashion. Level I studies include well-designed randomized controlled prospective studies (RCT). Level II include lower quality designed prospective RCT as well as prospective cohort studies. Level III include retrospective cohort studies and case-control studies. Level IV include case series. Level V include case reports, expert opinion, and personal observation. This is summarized in illustration A. The referenced article by Brighton et al is a review of how the level of evidence has evolved and how the different levels can carry varied amounts of impact on clinical treatments and future research.

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Question COMMENTS (3)

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

QID:513
1

Retrospective case control study

8%

(106/1332)

2

Prospective cohort study

86%

(1139/1332)

3

Case report of 3 patients with the same disease

1%

(8/1332)

4

High-quality randomized prospective clinical trial

6%

(75/1332)

5

The opinion of a review panel at the annual AAOS meeting

0%

(2/1332)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

Level II Evidence includes prospective cohort studies. There are 5 levels of evidence in clinical research. Level I includes randomized clinical trials. Level II includes prospective cohort studies. Level III includes case control studies AND retrospective cohort studies. Level IV includes case series. Level V evidence includes expert opinion, case reports, and personal observation. The cited reference by Bernstein et al is an excellent review of Evidence Based Medicine (EBM) and describes the 5 step process of making medical decisions based on the available, and often limited, evidence. These steps include: 1) Formulate answerable questions. 2) Gather the evidence. 3) Appraise the evidence. 4) Implement the evidence. 5) Evaluate the process. The reference by Spindler et al is another review article that discusses the different levels of evidence for different study types.


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