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Resources for nursing students

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)
Systematic 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-analysis Levels of evidence (sometimes called hierarchy 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".

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 systematic review, with or without meta-analysis

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

Level V
Based on experiential and non-research evidence.
      - 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
Dang, D., & Dearholt, S.L. (2018). Johns Hopkins nursing evidence-based practice : Model & guidelines (3rd ed). Sigma Theta Tau International.

Types of Resources

EBM Pyramid

  • 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

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

Study Types/Designs

Case Report - a write up of the case of an individual patient; a clinical presentation.  Often the first report of a new disease or disease trend.

Case Series - a write up of the cases of several patients all undergoing similar treatment.

Case-Control Study -  a comparison of study subjects with a particular disease/risk factor (cases) to those without (controls).  These have also been called retrospective studies.  A good design for rare diseases but easy to get poor data.

Clinical Trial - an experimental study in which subjects receive an intervention.  Preferably subjects are assigned to either treatment or no treatment/placebo (see Controlled Clinical Trial).  Some trials compare multiple treatments, e.g. the subjects could be assigned to: Treatment A, Treatment B, No treatment/placebo.  The different groups are called arms.   This is the best study design for testing effect of interventions.

Cohort Study -  a group of subjects followed through time.  Cohort studies can be used to track effect of an exposure, e.g. all subjects had been exposed to lead in their housing, or they can track a cohort not exposed.  They have also been called prospective studies.  This is a strong design for determining risk and incidence. 

Controlled Clinical Trial - a Clinical Trial where there is a control group receiving a comparison treatment or no treatment/placebo.

Cross Sectional Study - a descriptive study that documents the number of people with a particular disease or risk factor.

Randomized Controlled Trial - Same as Controlled Clinical Trial, with the added benefit of the subjects being randomly assigned to treatment/no treatment arms.  This avoids selection bias as all subjects have an equal chance of being assigned to any one of the treatment/no treatment arms.  Random assignment can be accomplished using machine generated random number tables.  Assigning subjects using methods such as coin tosses or assigning even-odd numbers is considered pseudo-randomization.