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Evidence Based Nursing Research: Evidence Hierarchy

Original page created by Karen Delorey at Bay Path Community College and edited for Westfield State University by Corinne Ebbs


Systematic Review: A systematic review  tries to identify, appraise, select and synthesize all RCTs (randomized control trials) relevant to a specific clinical question.  Stringent guidelines are set in order to draw a conclusion about whether or not there is conclusive evidence about a specfic treatment or topic.

Randomized Control Trial: An RCT is a clinical trial in which the subjects are randomly distributed into groups that are either subjected to the experimental procedure (such as use of a drug) or that serve as controls.  It is the research design considered to provide the most reliable evidence for evaluating the effectiveness of an intervention.

Meta-Analysis: A meta-analysis is a review that combines the quantitative (numbers) results from different studies on a defined intervention in order to obtain a quantitative estimate of the overall effect of the particular intervention.  A meta-analysis produces a stronger conclusion than can be provided by any individual study.

Practice Guideline: Clinical Practice Guidelines are practice recommendations based on rigorous review of the best evidence on a specific topic.

Cohort Study: A study designed to determine the relationship between a condition and a characteristic shared by some members of a group. The population selected is healthy at the beginning of the study. Some of the members of the group share a particular characteristic, such as cigarette smoking. The researcher follows the population group over a period of time, noting the rate at which a condition, such as lung cancer, occurs in the smokers and in the nonsmokers.

Case Control Study: A study where previously existing incidents of a medical condition are used in lieu of gathering new information. A group of patients with a particular disease or disorder, such as myocardial infarction, is compared with a control group of persons who have not had that medical problem. The two groups, matched for age, sex, and other personal data, are examined to determine which possible factor (e.g., cigarette smoking, coffee drinking) may account for the increased disease incidence in the case group.

Evidence Pyramid

This Evidence Hierarchy Pyramid is often used to graphically represent the quality of medical research. The higher on the pyramid the more comprehensive in scope, and more rigorous the methodology and peer review. You should be looking for the highest level of research available in EBP.

This guide will help you locate the highest levels of evidence: systematic reviews & meta-analyses, and practice guidelines. 

If you can't locate the highest levels of research to answer a specific clinical question you should use the highest level available.  Look for tutorials on searching reliable sources such as CINAHL, Medline, and PubMed databases for articles, studies and reports.

Systematic Reviews vs. Literature Reviews (Literature Reviews may be evidence-based, but they are NOT evidence (research).

  Systematic Review    Literature Review
Question            Focused on a single question.             Not necessarily focused on a single question,
but may describe an overview.
Protocol A peer review protocol or plan is included. No protocol is included.
Background Provides summary of literature on a topic. Provides summary of literature on a topic.
Objectives Clear objectives are identified. Objectives may or may not be identified.
Inclusion and
exclusion criteria
Criteria stated before the review is conducted. Criteria not specified.
Search Strategy Comprehensive search conducted in a systematic way. Strategy not explicitly stated.
Process of
selecting articles
Usually clear and explicit. Not described in a literature review.
Process of
evaluating articles
Comprehensive evaluation of study quality. Evaluation of study quality may or may not
explicit and clear.
Process of extracting
relevant information
Usually clear and specific. The process of extracting relevant
information is not explicit and clear.
Results and data
Clear summaries of studies based on
high quality evidence.

Summary based on studies where the quality of articles may not be specified.  May also be influenced by the reviewer's theories, needs and beliefs.

Discussion Written by an expert or group of
experts with a detailed and well
grounded knowledge of the issues.
Written by an expert or group of experts with a detailed and well
grounded knowledge of the issues.
Rating Evidence          Data from primary study may be 
synthesized in a meta-analysis. 
Evidence "grades" may be applied
to individual studies.
May use a level of evidence rating system to "grade" the quality and strength of
individual studies.

When evidence is lacking, the authors
usually recommend further research.

When evidence is lacking, the authors make recommendations based on their
opinions and experience.  Recommendations may be "graded" based on the
consistency and strength of the underlying evidence.

Adapted from: Bettany-Saltikov, J. (2010). Learning how to undertake a systematic review: Part 1. Nursing Standard, 24(40): 47-55.

Types of Evidence

More Definitions

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