When looking for information, consider the quality or reliability of the level of evidence of the results.
The image below shows the different levels of evidence and where to look for them.
Note this pyramid is mainly focused on medical & social science types of literature. In different fields the types of studies and levels of evidence available may differ. Aim to find the appropriate level of evidence for your discipline. Please ask your Liaison Librarian if you need more assistance.
Higher up the pyramid the amount of available literature on a given topic decreases, but the relevancy and quality of that literature increases. Systematic reviews and meta-analysis are considered to be the highest quality evidence on a research topic because their study design reduces bias and produces more reliable findings.
Source: Levels of Evidence Pyramid Adapted from image created by Andy Puro, September 2014.
[Click on image to see larger version]
Filtered information sources are sources that review, assess and evaluate a range of evidence sources.
- Meta Analysis: systematic review that uses quantitative methods to synthesize and summarize the results.
- Systematic Review: summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate statistical techniques to combine these valid studies.
- Critically Appraised Tools: clinical tools and guidelines where the evidence has been appraised to provide best practice information.
Unfiltered information sources are original research.
- Controlled Trials: Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest. They may or may not be Randomised - randomised have a higher level of evidence.
- Cohort Study: Involves identification of two groups (cohorts) of patients, one which received the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
- Case Controlled Study: A study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.
- Case Studies or Case Study Series: Report on a single patient or a series of patients with an outcome of interest. No control group is involved.
- Background information and Expert Opinion: Textbooks and sources without research
- Animal & In Vitro Studies: Laboratory experiment using animals or microorganisms, cells, or biological molecules to study the development and progression of diseases or to test treatments. Not as strong evidence as human physiology is different from the physiology of other animals, so may not have the same outcome or effect.
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