Evidence-Based Practice

When considering resources, it is important to understand how some research designs will produce stronger levels of evidence than others. This has led to the concept of hierarchy of evidence and levels of evidence. The hierarchy "provides a framework for ranking evidence that evaluates healthcare interventions and indicates which studies should be given the most weight in an evaluation where the same question has been examined using different types of study" (Akobeng, 2005, p. 840).

Hierarchies of evidence may be displayed in the form of a pyramid, a chart, or by assigning numbers and/or letters. There is no universal hierarchy of evidence; a number of hierarchies have been developed (Evans, 2003). However, systematic reviews, meta-analyses, and RCTs (randomized controlled trials) are generally considered the highest levels of evidence.

When looking at the types of research studies in the pyramid, you will notice that the filtered resources are near the top. As you continue down the pyramid, you will find unfiltered resources and background information. Filtered resources have gone through an extensive and systematic evaluation process. Examples include systematic reviews, critically-appraised topics, and critically-appraised articles. When conducting your research, you should try to find the highest quality evidence in systematic reviews and meta-analyses.

As the diagram demonstrates, the top of the pyramid is also the smallest. It may not be possible to answer every clinical question using the highest quality evidence from the top of the pyramid. It may be necessary to move down the pyramid in order to answer your question.

Background information and expert opinion (found in textbooks and other medical books) can be used to better familiarize yourself with a topic when beginning your research.

Next Step: Search the Evidence

Sources:

Akobeng, A. K. (2005). Understanding randomized controlled trials. Archives of Disease in Childhood, 90, 840-844.

Evans, D. (2003). Hierarchy of evidence: A framework for ranking evidence evaluating healthcare interventions. Journal of Clinical Nursing, 12, 77-84.

[Figure 1] EBM Pyramid and EBM Page Generator. (c) Copyright 2006-2011. Trustees of Dartmouth College and Yale University. All Rights Reserved. Produced by Jan Glover, David Izzo, Karen Odato, and Lei Wang.

Joanna Briggs Institute: Levels of Evidence
The Joanna Briggs Institute assigns a level of evidence to all conclusions drawn in JBI Systematic Reviews. Please note that Holy Family no longer subscribes to the JBI database.

Oxford Centre for Evidence-Based Medicine (CEBM): Levels of Evidence
The CEBM 'Levels of Evidence' document outlines an approach for different question types.

Filtered Resources

Systematic Review: Once many studies have been published on a particular topic, researchers and clinicians will systematically gather, evaluate, and appraise the findings into one document. Systematic reviews are different from literature reviews because they have clearly prescribed criteria for each step of the review process and they only include the most appropriate types of studies/data, yet they also are based on very wide, extensive searches of information. (Brown, 2009)

Integrated Research Review (IRR): Type of systematic review in which reviewer extracts findings from original studies, uses analytical reasoning to make conclusions, and presents conclusions in the form of narrative summaries. (Brown, 2009)

Meta-analysis: Type of systematic review in which reviewer uses quantitative methods and statistical techniques to combine results from different original studies. (Brown, 2009)

Critically Appraised Topic: Summary and evaluation of multiple research studies that focuses on answering a specific clinical question. (Heneghan & Badenoch, 2006)

Critically Appraised Article: Summary and evaluation of a single research study that focuses on answering a specific clinical question.

Unfiltered Resources

Randomized Controlled Trials (RCT): Experimental studies that represent advanced testing of an intervention. They have defined study protocols and typically large, diverse samples. (Brown, 2009)

Cohort Study: A study in which a sample is drawn from a larger population. The sample is divided into two groups (called cohorts): one with the risk factor or exposure and one without. The cohorts are followed for a period of time and outcomes are assessed and compared. (Brown, 2009)

Case-Control Study: A study that identifies persons with and without a particular outcome of interest and looks backward in the history of the two groups to identify possible causes. Unlike cohort studies that identify risks and monitor outcomes, case-control studies identify outcomes and work backward to identify possible causes of those outcomes. (Brown, 2009)

Background Information / Expert Opinion: Use background information from textbooks and other medical books to better familiarize yourself with a topic before beginning your research or as needed throughout the research process.

Sources:

Brown S. (2009). Evidence-based nursing: The research-practice connection. Sudbury, MA: Jones and Bartlett.

Heneghan, C. & Badenoch, D. (2006). Evidence-based medicine toolkit. Malden, MA: Oxford.