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Levels of Evidence: Levels of Evidence

links and tips for finding information related to evidence based nursing practice

Systematic Review articles present evidence gathered from the review of previously published studies. They may include only randomized controlled trials (level 1 evidence) or a wider variety of studies (level 5 evidence).

Look for key words including:

  • Systematic Review
  • Meta-Synthesis
  • Meta-Analysis

Also review abstracts and articles to determine if the review uses randomized controlled trials and counts as level 1 evidence or uses a wider variety of studies and counts as level 5 evidence.

 

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Controlled trial articles describe a single study of an intervention which is carried out on one group and compared to a second "control" group to draw conclusions about the effectiveness of the intervention.

Controlled trials may be randomized (level 2) or non-randomized (level 3).

Look for key words including:

  • Randomized Controlled Trials
  • Controlled Trials
  • Clinical Controlled Trial
  • Treatment Outcome/Clinical Trial

Also review abstracts and articles to determine if the trial uses randomization and counts as level 2 evidence or does not use randomization and counts as level 3 evidence.

 

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Case Control Study articles present observations comparing "case" patients with a condition to "control" patients without the condition.

Cohort Study articles present observations over time of groups or "cohorts" of people to evaluate outcomes based on common experiences.

Look for key words including:

  • Case Control Study
  • Cohort Study
  • Retrospective Cohort Study
  • Prospective Cohort Study

 

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Descriptive studies do not include an experiment or intervention.

Case report articles provide a profile of a subject or group of subjects with a condition of interest.

Cross-sectional studies provide a profile of a disease or condition in a specific population.

Qualitative studies focus on experiences, stories, or perspectives of the subjects.

Look for key words including:

  • Descriptive
  • Qualitative
  • Experiences
  • Perspectives
  • Ethnography
  • Grounded Theory

Also review abstracts and articles to determine if the methods described are descriptive or qualitative.

 

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Expert opinion appears in the literature as editorials and commentaries.

Look for key words including:

  • Editorial
  • Commentary
  • Communication
  • Comment

 

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Definitions

  1. Systematic review & meta-analysis of randomized controlled trials; clinical guidelines based on systematic reviews or meta-analyses
  2. One or more randomized controlled trials
  3. Controlled trial (no randomization)
  4. Case-control or cohort study
  5. Systematic review of descriptive & qualitative studies
  6. Single descriptive or qualitative study
  7. Expert opinion

Source: Melnyk, B.M. & Fineout-Overholt, E. (2011). Evidence-based practice in nursing and healthcare: A guide to best practice. Philadelphia: Lippincott, Williams & Wilkins.