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Searching for Health Sciences Research

Learn how to create a searchable question to find and access literature to help answer your clinical question.

Types of Research

In the Health Sciences, we generally categorize evidence into two main types: Filtered and Unfiltered resources. When you look at the traditional evidence pyramid, we are looking at the research cycle: starting with unfiltered information (the original research), once a body of work is established, we can start analyzing and synthesizing the existing research, creating filtered information (i.e., systematic reviews and meta-analyses). 

Image from

But in reality, this pyramid is looking at journal articles, and represents just a small part of the entire body of evidence. This evidence pyramid shows how evidence expands beyond traditional published research:

From the University of Michigan, modified from:  Haynes RB. Of studies, syntheses, synopses, summaries and systems: the “5S" evolution of services for evidence-based health care decisions. ACP J Club. 2006 Nov-Dec;145(3):A8-9. 

Unfiltered (Primary / Original Research)

In the sciences, a primary source is a source that includes original research that's documented at the time of study. A primary source will generally have a Methods section that describes the researchers' procedures and materials. Primary sources can take the form of:

  • original research article
  • scholarly journal article
  • academic journal article
  • thesis or dissertation
  • conference paper
  • lab notebook

Filtered (Secondary Sources / Reviews)

Secondary sources offer analysis, evaluation, interpretation and/or synthesis of primary sources. A secondary source could be:

  • review article
  • literature review
  • systematic review
  • meta-analysis
  • editorial
  • book or product review
  • monograph (book) or book chapter
  • conference proceedings (collections of conference papers)

Filtered (Tertiary Sources)

Tertiary sources offer summaries or compilations of information from primary and secondary sources. A tertiary source could be:

  • encyclopedia, dictionary or handbook
  • textbook
  • bibliography
  • evidence-based care sheet
  • survey article

Suggested Research Designs

Systematic Reviews and Meta-Analyses are generally considered to be the highest quality of evidence. But the type of study you need may differ based on what type of research question you are trying to answer. You'll want to identify which are the most valid research designs that can "prove" the research question with the understanding that there may not be much research done on that research question.

Clinical Question

Suggested Research Design(s)

All Clinical Questions

Systematic review, meta-analysis


Randomized controlled trial (RCT), meta-analysis
Also: cohort study, case-control study, case series


Randomized controlled trial (RCT), meta-analysis, cohort study
Also: case-control study, case series


Randomized controlled trial (RCT)
Also: cohort study


Randomized controlled trial (RCT), meta-analysis
Also: prospective study, cohort study, case-control study, case series


Cohort study

Also: case-control study, case series


Qualitative study

Quality Improvement

Randomized controlled trial (RCT)
Also: qualitative study


Economic evaluation

Table source: OHSU's Evidence-Based Practice Toolkit for Nursing

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