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Systematic Review

Filtered Information vs. Unfiltered Information

Filtered Information - Information that has been collected and aggregated by expert analysis and review. The quality of the studies has already been appraised and recommendations for practice may have already been made. Examples include meta-analyses and systematic reviews

Unfiltered Information - Primary or original research studies. Original research studies that have not yet been synthesized or aggregated such as randomized controlled trials (RCTs), cohort studies and case-control studies, which are often published in peer-reviewed journals. These studies have not undergone additional analysis and review beyond that of the peer review process for each study.

Source: OPEN MD

Hierarchy of Evidence

Source: OPEN MD

Study Designs


A systematic review that uses quantitative methods to synthesize and summarize the results.

Systematic Review

A 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.

Randomized Controlled Trial

Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest.

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.

Cross-sectional study

The observation of a defined population at a single point in time or time interval. Exposure and outcome are determined simultaneously.

Case-Control 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 series

A report on a series of patients with an outcome of interest. No control group is involved.




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