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EXS290: Introduction to Evidence-Based Practice (Fried)

Primary vs. secondary Sources

A primary source is a direct source of information. Articles reporting on a study that was directly conducted by the authors may be considered primary sources, as the researchers are reporting more or less directly to you without others' interpretations getting in between.

A secondary source is a mediated or interpreted source of information. Meta-analyses, for instance, pool the results of many different individual studies and view the different conclusions in relation to each other to make broad conclusions and observations based on a very large number of results.

Levels of Evidence



  • Lower levels of evidence include qualitative and non-experimental studies, and those that are subject to a lower level of critical appraisal.
  • Higher levels correspond to studies involving an increased degree of critical appraisal, quantitative analysis, review, assessment, and more stringent scientific methodologies.
  • The top of the pyramid represents studies subject to the highest level of critical appraisal and analysis, and corresponds to the very small proportion of all the nursing and medicine literature that lends itself to answering specific clinical questions, whether in the form of systematic reviews, meta-analyses or an evidence-based guideline resulting from combined analysis and appraisal of available evidence from all eligible sources.

Source: DePaul University Library, Evidence-Based Nursing Research Guide:


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