Introduction to evidence-based practice for the health sciences

Levels of evidence

When searching for evidence to answer a clinical question, you need to understand the levels of research evidence available. In general, best practice states that you should search for the highest quality of evidence as this means that the information used is accurate, trustworthy, and founded in sound research methods. In healthcare, there are two broad categories of evidence - primary and secondary.

Secondary information

This can also be called filtered information and includes analyses, syntheses, interpretations, commentaries, and evaluations of original research studies. Secondary information refers to research that has been critically assessed, summarised, and synthesised to provide high-quality evidence to support decision-making. This is considered to be the highest quality of evidence. 

You can find this kind of evidence in specialised EBP resources such as the Cochrane Database of Systematic Reviews, part of the Cochrane Library, or the JBI EBP Database, or in more general health & medical databases such as CINAHL, PubMed, or PsycINFO.

To learn more about the databases that are specific to your area of study, visit the Search the databases section of your discipline-specific libguide.

Primary information

This is also known as unfiltered information and includes original analysis and data from original research studies. No external analysis, evaluation, or appraisal has been applied to these resources. 

The evidence pyramid

Evidence can be ranked according to its quality. The evidence pyramid shows different types of evidence according to their methodological strength, with the most reliable evidence at the top. The further down the pyramid, the lower the quality of evidence. Unless you have been instructed otherwise, you should try to find the highest level of evidence related to your search topic. 

EBM pyramid and EBM page generator. © 2006 Trustees of Dartmouth College and Yale University. All rights reserved. Produced by Jan Glover, David Izzo, Karen Odato, and Lei Wang. 

Visit the Types of study page in this guide to learn more about the different types of research study included in the evidence pyramid. 

Beyond the evidence pyramid

While the evidence pyramid focuses on research studies, healthcare professionals often rely on additional resources that synthesise and apply evidence to real-world practice. These include clinical practice guidelines, clinical procedures, and factsheets, which help bridge the gap between research and decision-making.

• Clinical practice guidelines are recommendations developed by expert panels based on the highest levels of evidence. They provide best practice advice for diagnosis, treatment, and patient care. 
• Clinical procedures & protocols are standardised, step-by-step instructions for performing healthcare procedures or treatments. They ensure consistency and support patient safety in healthcare settings.
• Factsheets and patient information resources are brief, plain-language documents that summarise health conditions, treatments, or advice. They are designed to be quick reference resources for healthcare professionals and patients.

While these resources simplify evidence to support their application in practice, it is essential to ensure they are current, reliable, and based on high-quality research. 

References

Glover, J., Izzo, D., Odato, K., & Wang, L. (2006). EBM Pyramid. http://www.ebmpyramid.org/images/pyramid.gif