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Hierarchies and levels of evidence

Before you start searching you need to know not all research is the same. You don't want just any type of article and any type of research methodology for EBP.

You want reliable and unbiased research.

In most cases this means you are ideally looking for a type of study known as a systematic review (or even better a systematic review with a meta-analysis for a quantitative review, a meta-synthesis for a qualitative one). These are higher tier evidence sources (sometimes referred to as secondary studies ie studies that combine and appraise collections of usually single or primary research on a particular topic or question). There are also umbrella reviews also known as reviews of systematic reviews.

If there are no recent systematic reviews or meta-analyses and your topic relates to treatment or therapy, look for a randomised controlled trial, or the next best and appropriate primary study. For example it may not be ethically appropriate to do an rct, or some studies use case-control or cross-sectional methods. Although not a study type in the true sense clinical practice guidelines are often a 'go to' resource in EBP.

There is also a pyramid for qualitative research 1.

The pyramid is only one example of levels of evidence. For others see:

The Centre for Evidence Based medicine at Oxford also has a handy study design tree.


1. Daly J, Willis K, Small R, Green J, Welch N, Kealy M, et al. A hierarchy of evidence for assessing qualitative health research. Journal of Clinical Epidemiology. 2007;60(1):43-9. 10.1016/j.jclinepi.2006.03.014.

What is an RCT and what is a Systematic Review?

Additional study types

Watch these videos

Study types

Finding the best level of evidence in health research.
University of Sydney Library

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