Secondary literature: Summaries or interpretations of original research

Grey literature: Research that is not formally published in peer-reviewed journals

Primary

literature: Government reports and policy documents

Secondary literature: Original research articles presenting new data

Grey literature: Review articles summarizing multiple studies

Primary

literature: Research reports, reviews, and meta-analyses

Secondary literature: Unpublished research like theses and conference papers

Grey literature: Original research articles presenting new data or findings

Primary

literature: Summaries or interpretations of original research written by

someone other than the original researcher

Secondary literature: Original research articles presenting new data or

findings

Grey literature: Research published in peer-reviewed journals only