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.
Source: DePaul University Library, Evidence-Based Nursing Research Guide: https://libguides.depaul.edu/ebp
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