Think of the levels of evidence as a pyramid. In fact, you may see models of an "Evidence-Based Medicine Pyramid" -- there are a few! There is probably not going to be as much level one or high-quality research evidence as there will be level four or five evidence. It is up to you to evaluate and appraise.
First, it's important to understand how to tackle the information that can be found in a research paper. This open access article from Carey et al. presents ten simple rules for understanding a research paper.
Carey, M. A., Steiner, K. L., & Petri, W. A., Jr (2020). Ten simple rules for reading a scientific paper. PLoS Computational Biology, 16(7), e1008032. DOI link: https://doi.org/10.1371/journal.pcbi.1008032; PubMed Central Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7392212/
It is absolutely critical that you evaluate the evidence you've identified. Not all published research is without flaws. Fortunately, there are a handful of wonderful tools to help you appraise the evidence. To get started, see if these collections contain a checklist for the kind of study you've identified, and follow the prompts on the checklist:
It will be helpful for you to understand levels of evidence. Different kinds of evidence are better for answering different types of clinical questions. There are different iterations of evidence-based medicine pyramids or hierarchies.
Here is an example of evidence levels from the Centre for Evidence-Based Medicine at the University of Oxford for therapy / prevention, etiology / harm:
| Level 1a | Systematic Reviews (with homogeneity) of randomized controlled trials |
| Level 1b | Individual Randomized Controlled Trials |
| Level 1c | All or none randomized controlled trials |
| Level 2a | Systematic Reviews (with homogeneity) of cohort studies |
| Level 2b | Individual cohort studies |
| Level 2c | "Outcomes" Research |
| Level 3a | Systematic Reviews (with homogeneity) of case-control studies |
| Level 3b | Individual case-control studies |
| Level 4 | Case-series |
| Level 5 | Expert opinion without explicit critical appraisal or based on bench research |
Produced by Bob Phillips, Chris Ball, Dave Sackett, Doug Badenoch, Sharon Straus, Brian Haynes, Martin Dawes since November 1998. Updated by Jeremy Howick March 2009. https://www.cebm.net/2009/06/oxford-centre-evidence-based-medicine-levels-evidence-march-2009/
Here is an example of an abridged evidence-based medicine hierarchy from the Johns Hopkins Nursing Evidence Based Practice Model:
| Level I | Experimental studies, systematic reviews of randomized controlled trials |
| Level II | Quasi-experimental studies, mixed methods, systematic reviews of randomized controlled trials and quasi-experimental studies |
| Level III | Non-experimental studies, systematic reviews of randomized, quasi-, and non-experimental studies, mixed methods, qualitative meta-analysis |
| Level IV | Expert opinions, clinical practice guidelines, position statements |
| Level V | Traditional narrative literature reviews, quality improvement, case reports, opinions based on anecdotal evidence |
Dang, D., & Dearholt, S. L. (2017). Johns Hopkins Nursing Evidence-Based Practice Third Edition. Indianapolis: Sigma Theta Tau International. https://www.worldcat.org/title/johns-hopkins-nursing-evidence-based-practice-model-and-guidelines/oclc/1001413926.
You can always use the basic ideas represented in these evaluation frameworks to perform an overall evaluation.
From the McIntyre Library at the University of Wisconsin, Eau Claire
By now, you should have identified and read some articles or evidence. How do you determine that the evidence is sound?
Open up a Word document, get a blank sheet of paper, or use the document you started in the previous steps. Answer the following questions:
