For clinical questions, articles with the highest quality of evidence are best. The pyramid represents the Levels of Evidence Hierarchy. Studies are assigned to a level based on their design and strength of recommendation.
Source: Wood, G. L, & Haber, J. (2014). Nursing research: Methods and critical appraisal of evidence-based practice (8ed). St. Louis: Mosby/Elsevier
Types of studies
Level I
- Clinical Practice Guideline: Recommendations for clinicians based on a systematic review of evidence.
- Meta-Analysis: Combines the results of studies using quantitative methods to statistically estimate the effects of proposed interventions.
- Systematic Review: Appraised summary of all experimental or quantitative research addressing a specific clinical question.
Level II
- Randomized Controlled Trials: A randomized group of patients are assigned to an experimental group and a control group. These groups are followed up on for the variables/outcomes of interest.
Level III
- Quasi-experimental Trial: Controlled trial with a nonrandomized group of patients.
Level IV
- Cohort Study: Identifies two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not. Follows the cohorts forward for the outcome of interest.
- Case-Control Study: Identifies patients who have the outcome of interest (cases) and control patients without the same outcome and looks for exposure of interest.
Level V
- Systematic Review: Appraised summary of all qualitative or descriptive research that addresses a specific clinical question.
Level VI
- Case Report: Evidence form a single descriptive or qualitative study
Level VII
- Expert Opinion: Descriptive study of a single case or series of cases with no research design or generalized information found in textbooks, encyclopedias, etc.
