Nursing

Library resources for the School of Nursing

Levels of Evidence

Levels of evidence are assigned to studies based on the methodological quality of their design, validity, and applicability to patient care. These decisions gives the "grade (or strength) of recommendation.

Johns Hopkins Nursing EBP: Levels of Evidence

Level I
Experimental study, randomized controlled trial (RCT)
Systematice review of RCTs, with or without meta-analysis

Level II
Quasi-experimental Study
Systematic review of a combination of RCTs and quasi-experimental, or quasi-experimental studies only, with or without meta-analysLevels of evidence (sometimes called heirarchy of evidence) are assigned to studies based on the methodological quality of their design, validity, and applicability to patient care. These decisions gives the "grade (or strength) of recommendation".
is.

Level III
Non-experimental study
Systematic review of a combination of RCTs, quasi-experimental and non-experimental, or non-experimental studies only, with or without meta-analysis.
Qualitative study or systematice review, with or without meta-analysis

Level IV
Opinion of respected authorities and/or nationally recognized expert committees/consensus panels based on scientific evidence.
    Includes:
         - Clinical practice guidelines
         - Consensus panels

Level V
Based on experiential and non-research evidence.
    Includes:
      - Literature reviews
      - Quality improvement, program or financial evaluation
      - Case reports
      - Opinion of nationally recognized expert(s) based on experiential evidence

Greenhalgh, Trisha.  How to Read a Paper: the Basics of Evidence Based Medicine.  London: BMJ, 2000.

From Johns Hopkins nursing evidence-based practice : Models and Guidelines
Dearholt, S., Dang, Deborah, & Sigma Theta Tau International. (2012). Johns Hopkins Nursing Evidence-based Practice : Models and Guidelines.

Types of Resources

The systematic review or meta-analysis of randomized controlled trials (RCTs) and evidence-based practice guidelines are considered to be the strongest level of evidence on which to guide practice decisions. (Melnyk, 2004) The weakest level of evidence is the opinion from authorities and/or reports of expert committees.

Systematic reviews, meta-analyses, and critically-appraised topics/articles have all gone through an evaluation process: they have been "filtered". 

Information that has not been critically appraised is considered "unfiltered".

As you move up the pyramid, however, fewer studies are available; it's important to recognize that high levels of evidence may not exist for your clinical question.  If this is the case, you'll need to move down the pyramid if your quest for resources at the top of the pyramid is unsuccessful.

EBP Pyramid

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  • Meta-Analysis  A systematic review that uses quantitative methods to summarize the results.
  • Systematic Review    An article in which the authors have systematically searched for, appraised, and summarized all of the medical literature for a specific topic.
  • Critically Appraised Topic     Authors of critically-appraised topics evaluate and synthesize multiple research studies.
  • Critically Appraised Articles  Authors of critically-appraised individual articles evaluate and synopsize individual research studies.
  • Randomized Controlled Trials  RCT's include a randomized group of patients in an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.
  • Cohort Study  Identifies two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
  • Case-Control Study  Involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking to see if they had the exposure of interest.
  • Background Information / Expert Opinion   Handbooks, encyclopedias, and textbooks often provide a good foundation or introduction and often include generalized information about a condition.  While background information presents a convenient summary, often it takes about three years for this type of literature to be published.
  • Animal Research / Lab Studies  Information begins at the bottom of the pyramid: this is where ideas and laboratory research takes place. Ideas turn into therapies and diagnostic tools, which then are tested with lab models and
    animals.

Sources:
Greenhalgh, Trisha.  How to Read a Paper: the Basics of Evidence Based Medicine.  London: BMJ, 2000.
Glover, Jan; Izzo, David; Odato, Karen & Lei Wang. EBM Pyramid.  Dartmouth University/Yale University. 2006.