Primary research:Peer-reviewed articles written by authors (scientists or researchers) who actually performed an original experiment or are reporting their ﬁeld observations, i.e., of organisms or medical patients.
Secondary research: Peer-reviewed articles written by authors (also scientists and researchers) who summarize or discuss trends in the primary literature. In the sciences, these are called "review" articles.
Tertiary research: Non‐peer-reviewed articles, books, newspaper articles, encyclopedia entries, etc. These are often written by journalists who summarize the highly technical scientific literature for a general audience. They will reference or link to the primary research.