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A guide to help you get started with library research.



Types and Levels of Sources

The types of sources you use in your research is important. Not all information is created equally. There are better sources for different types of information needs.

Once you have defined your topic and research question consider:

  • The information cycle (how information is produced and disseminated over time after an event) 

  • Type of source

    • Primary, Secondary or Tertiary

    • Scholarly/Peer-Reviewed or Not

  • Level of evidence

    • Systematic review

    • Randomized Controlled Trials

    • Studies

Information Cycle

Knowing how and when information is published along the information cycle can help you select the right type of resource. 

Know Your Sources

This tool provides a brief description of each type of source and breaks down 6 factors of what to consider when selecting a source.

Primary, Secondary and Tertiary Sources

Sources fall into three main categories, primary, secondary and tertiary.

Primary sources give firsthand accounts or direct evidence regarding the event. They are writings contemporary to what is being researched.

Secondary sources discuss information presented elsewhere. It is created later, after the event, by someone who did not participate or experience the event. Most scholarly articles and books are secondary sources.

Tertiary sources consolidate and summarize primary and secondary sources. For example, encyclopedias and factbooks are considered tertiary (although some may be secondary).

Scholarly Articles and Peer-Review

Sources are created for different audiences. Sources created by scholars for other scholars are often published in scholarly/peer-reviewed journals.

Peer-review is a vetting process a source may go through. The peer-review process involves an author submitting their work for review, then a group of their "peers" (other people working in the same field) evaluate the work for quality and meeting scientific standards. Then the work is returned to the original author for edits/revisions. Then the work is (hopefully) re-submitted and accepted for publishing.

The peer-review process is not perfect and academic publishing is highly competitive so problems do occur. You can read about some of the conversations about revising peer-review in the following articles: Scientists Aim To Pull Peer Review Out Of The 17th CenturyThe Future of Peer Review and When reviewing goes wrong: the ugly side of peer review.

There are several features of scholarly sources that distinguish them from popular sources including:

  • Written for experts by experts

  • Use of professional language for the discipline

  • Based on original research or analysis of previous research

  • Contains citations

  • No attractive packaging or ads

  • Scientific paper format (abstract, introduction, methods, results, discussion, conclusion, references)

  • Peer-reviewed

  • Published by academic publisher

how to read scholarly articles libguide link

Levels of Evidence

In health sciences and medicine, sources also have a level of evidence based on the type of research conducted for the work. The levels of evidence are described in a pyramid with the lowest level of evidence at the bottom and the highest level of evidence at the top. The amount of sources meeting the criteria of these levels decreases as the levels increase so that there are a lot more level VII sources than level I sources.

Rating System for the Hierarchy of Evidence for Intervention/Treatment Questions The following leveling system is from Evidence-Based Practice in Nursing and Healthcare: A Guide to Best Practice (2nd ed.) by Bernadette Mazurek Melnyk and Ellen Fineout-Overholt. Level I: Evidence from a systematic review or meta-analysis of all relevant randomized controlled trials (RCTs) Level II: Evidence obtained from well-designed RCTs Level III: Evidence obtained from well-designed controlled trials without randomization Level IV: Evidence from well-designed case-control and cohort studies Level V: Evidence from systematic reviews of descriptive and qualitative studies Level VI: Evidence from single descriptive or qualitative studies Level VII: Evidence from the opinion of authorities and/or reports of expert committees Modified from Guyatt, G. & Rennie, D. (2002). Users' Guides to the Medical Literature. Chicago, IL: American Medical Association; Harris, R.P., Hefland, M., Woolf, S.H., Lohr, K.N., Mulrow, C.D., Teutsch, S.M., et al. (2001). Current Methods of the U.S. Preventive Services Task Force: A Review of the Process. American Journal of Preventive Medicine, 20, 21-35.


The level of evidence can usually be discovered in the methods section of the article. Some authors will state exactly what type of study the article is about and for other sources, the reader will have to determine the study type.

Use this chart to help determine the level


Level I is a systematic review and Level VII is an expert opinion.

Another library has created a guide with even more information. Check it out at the link below.

You can also use this handy chart from the University of New Mexico.

Theoretical Models and Frameworks

Theoretical Models and Frameworks create a structure and vision for the study. You can think of these as blueprints for the study. A scientific study will use a theoretical framework or model to guide the design of the study. 

Types of Clinical Research

  • Action research

  • Case study

  • Casual

  • Cross-Sectional

  • Cohort

  • Descriptive

  • Experimental 

  • Exploratory

  • Historical

  • Longitudinal

  • Meta-Analysis

  • Mixed Methods

  • Observational

  • Philosophical

How to support Research with Theoretical and Conceptual Frameworks


Learn more at