Primary Literature: Original Research Articles
Describe the findings of original observations or experiments ~~ Should provide an abstract, methods, data/results, and points for discussion. --> Peer review process is integral to the quality and integrity of original research.
Secondary Literature: Review articles, Systematic Reviews, and Meta-analyses
Summarize current research in a particular area of study, categorizing and highlighting recent research studies ~~ Systematic reviews such as the Cochrane Database of Systematic Reviews use systematic methods to collect, appraise and synthesize original research findings.
-> Considered scholarly and a high level of evidence, technically not peer reviewed but fine for research assignments unless your instructor has specified you need to use original research.
Tertiary Literature: Textbooks, Wikipedia, Medline Plus, Encyclopedias
Compiled from primary and secondary sources to provide information at an introductory level. ~~ Once you have an overview of an unfamiliar topic, you are better equipped to start looking for scholarly articles in journals. ~~ The quality and credibility of tertiary sources varies widely depending on the sponsoring organization, authors, intended audience, etc.
--> Good quality resources may contain credible information but they are NOT considered peer-reviewed.