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Guide to the Basics

A brief overview of the resources available at the Library of Rush University Medical Center

Types of Sources - Primary, Secondary and Tertiary

Types of Medical Literature

Medical literature is often classified based on how far removed the information is from the original source.

Primary Literature/Source
Primary sources are original materials.  It is authored by researchers, contains original research data, and is usually published in a peer-reviewed journal. Primary literature may also include conference papers, pre-prints, or preliminary reports.

Secondary Literature/Source 
Secondary literature consists of interpretations and evaluations that are derived from or refer to the primary source literature. Examples include review articles (e.g., meta-analysis and systematic reviews) and reference works. Professionals within each discipline take the primary literature and synthesize, generalize, and integrate new research.

Tertiary Literature/Source
Tertiary literature consists of a distillation and collection of primary and secondary sources such as textbooks, encyclopedia articles, and guidebooks or handbooks. The purpose of tertiary literature is to provide an overview of key research findings and an introduction to principles and practices within the discipline.

  Primary Literature/Source Secondary Literature/Source Tertiary Literature/Source 

What is it?       


Original research results in journals, dissertations, conference proceedings, correspondence

Abstracting and indexing services, review articles, systematic reviews, meta-analysis, practice guidelines

Text books, encyclopedias,   handbooks, newspapers

Example of where you can  find it peer-reviewed journals Cochrane Library AccessMedicine for Consumers

Adapted from the Information Services Department of the Library of the Health Sciences-Chicago, University of Illinois at Chicago.

One more way to look at it:   Six Degrees of Separation (or Six Degrees of Kevin Bacon)

  • Primary Literature/Source:  someone talked to Kevin Bacon and wrote about it
  • Secondary Literature/Source:  someone else read the above article and summarized it for a radio show
  • Tertiary Literature/Source:  a magazine included a mention of the article in a summary of Kevin Bacon interviews

Types of Reviews - Literature and Systematic

Literature Review

Have you been asked to do a "literature review" as part of a research assignment?  It's best to check with your instructor to make sure you're 100% clear on what he/she means by "literature review."  Here's the classic definition:

Definition: A literature review is an assessment of a body of research that addresses a research question.  "Literature" can mean any type of written material.  Be sure to include a large number of sources (often your instructor will give you a range).

Purpose:  A literature review identifies what is already known about an area of study.  It may also identify questions a body of research does not answer, or make a case for why further study of research questions is important to a field.  It's not an opinion piece;  it's a summarization of the articles you read.


Check out the link below for a comprehensive look at literature searches, courtesy of the Writing Center at UNC Chapel Hill.


Systematic Reviews

A systematic review aims to provide a comprehensive, exhaustive summary of current literature relevant to a research question. These reviews are conducted by a team of people and can take up to a year (or more) to complete.  The Cochrane Database of Systematic Reviews is available to Rush affiliates and is an excellent source of evidence-based medicine.  For more information on systematic reviews, click the link below.

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