Evaluate Information

Primary sources

A primary source represents a piece of original work. In the sciences this can mean the original data. In many other disciplines this can mean fully original writings, artworks, and so forth. 

• In the sciences: this kind of source still discusses the past work of others, but as a backdrop for new data collection and analysis.
• In other disciplines: this kind of source may, instead, reflect personal creation or expression. 
• In a primary source in the sciences, the abstract may make clear the authors’ role in collecting the raw data (“we collected” or “sampled” or “observed”).
• In other disciplines, the format may vary widely, and the source may not include an abstract. 

Secondary sources 

This kind of resource is somewhat more common. 

• This kind of source will reflect on, summarize/synthesize, or review/critique existing work or a primary source. 
• The abstract or title may include terms like “review” (of which there are many types) or “meta-analysis.”
• In humanities and arts disciplines, especially, the abstract may instead focus closely on what is being analyzed or discussed (such as literary work's title, or the name of a musical composer). 

Peer Reviewed Articles

In short, this means that the work has been vetted by professional peer experts. This is often a kind of a "blind"  or "double blind" process, where the author does not know the identity of the reviewers, and the reviewers don't know the identity of the author(s). For a quick overview of peer review, see the short video "Peer Review in Three Minutes," from NC State University Libraries. 

Scholarly published sources

These are commonly formally peer-reviewed articles in what may be sometimes called refereed journals. In some disciplines, the formal process of peer-review may also be demonstrated in book chapters or books and even some trade publications. The peer-review process is part of what typically  indicates a source is "scholarly" in many contexts. In some contexts, though, resources that do not fully go through this process (like dissertations) may still be considered "scholarly". 

This kind of source is written for expert audience; may use precise and specialized language.

• It is thoroughly cited (in-text and at the end). 
• It attends to shortcomings or limitations and not only successes.
• It aims to avoid and/or make clear any bias or conflict of interest.
• Some scholarly published articles in some disciplines may present an argument with evidence (such as from the literature) to defend it. Scientific publications may, instead, focus on clarity and precision in order to present findings. 

Grey Literature 

These may be reports (such as governmental or market research); conference proceedings; theses; working papers (sometimes called white papers); professional (disciplinary or society) news blasts and even blog posts; policy statements.

Popular Literature

This can be in formats similar to the above examples - articles, blog posts, and even books. 

• This kind of source is written for a general rather than expert or specialized audience, so it should avoid or take care to explain technical language. 
• The editing is more likely to focus on aspects of style and less likely to rigorously test the science or vet all sources (the extent is somewhat dependent on the publication). 
• The writing style may be more creative than in traditional scholarly literature; Even scientific popular literature may be presented in a persuasive manner or as a kind of argument. 
• Frequently, formal citations will not be included.

Credits

Content adapted from The University of Washington Tacoma Library. "About Scientific Literature." Biology Libguide. Updated January 9, 2025. https://guides.lib.uw.edu/tacoma/biology

NC State University Libraries. (Oct 1, 2014).  "Peer Review in Three Minutes." [Video] https://www.lib.ncsu.edu/videos/peer-review-three-minutes

Scholarly Journals

• written for experts and academics
• in print contains few if any ads or illustrations    
• will have footnotes, bibliography, or a works cites    
• written by experts in the field    
• generally peer reviewed by a field of experts    
• articles will generally include an abstract    
• Examples: American Journal of Psychology, New England Journal of Medicine, Wisconsin Studies in Contemporary Literature    

Popular Magazines

• written for a general audience    
• in print contains many ads and illustrations    
• usually do not have a works cited or bibliography    
• written by journalists, editorial staff, and freelancers    
• only reviewed by editorial board    
• will not have an abstract    
• Examples: Newsweek, National Geographic, Cosmo    

Trade Journals

• written for a specific industry
• may contain ads or illustrations
• may have a bibliography
• may be written by experts
• may or may not be reviewed
• may not have an abstract
• Examples: Advertising Age, Food Trade Review, Popular Mechanics
   

It's all about context...

Determining the difference between a primary and secondary source is tricky because it all comes back to your research question. The difference can also vary across disciplines.

Check out this helpful chart from the Indiana University Indianapolis Library for more examples.

Primary Sources

• original research    
• first hand account of an event    
• could be a newspaper article, a diary entry, an original work of art, a lab report, a blog, a speech, etc.    
• factual, not interpretive    

Secondary Sources

• analysis of past research
• interprets a primary source, interprets a creative work, a second hand account of an event
• could be biographies, history, literary criticism, a review of a clinical trial, conference proceedings, etc.
• factual and/or interpretive