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Albert S. Cook Library


Learn about resources related to nursing research and coursework.

Getting Started

What is Evidence?

In the context of a literature review, class paper, thesis, or dissertation, "evidence" can refer to a wide array of sources. Merriam-Webster Dictionary defines evidence as:

something that furnishes proof

"Evidence." 2020. In

What is Evidence-Based Medicine?

…the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research.

Sackett, D. L., Rosenberg, W. M., Gray, J. A., Haynes, R. B., & Richardson, W. S. (1996). Evidence based medicine: what it is and what it isn't. BMJ (Clinical research ed.), 312(7023), 71–72.

Evidence in the Health Professions

David Sackett, widely considered one of the fathers of evidence-based medicine, called on the clinical community to use the best available evidence in decision-making. Different types of studies or trials may answer different types of questions. See more about evidence hierarchies and levels of evidence in the Evidence Appraisal section.

Searching for Evidence

Searching for evidence in a bibliographic literature database is a balance of trial and error, intuition, and practice. If you take the time to start off right, keep an open mind, and follow the appropriate steps, you’re bound to find success. Use the ABCDE Research Inquiry Framework (Price, et al., 2020) to approach literature searching in an effective and reproducible manner.

Price, C., Kudchadkar, S. R., Basyal, P. S., Nelliot, A., Smith, M., Friedman, M., & Needham, D. M. (2020). Librarian integration into health care conferences: a case report. Journal of the Medical Library Association: JMLA, 108(2), 278.

The framework below uses ABCDE to guide you through the searching process.

A: Assess Topic, Scope, and Goals

B: Brainstorm Keywords

C: Choose Databases and Resources to Search

D: Document the Search

E: Evaluate the Evidence

A: Assess Your Topic, Scope, and Goals

icon of the letter AAssess Your Topic, Scope, and Goals

Assess the topic, scope, and goals of your project. If your goal is a literature review, understand the type of literature review and the methodology involved. This step is a good time to do some preliminary background searching to get an idea of what’s already been done. Hint: look for a question development framework that will help you frame your topic.

Formulating Your Research Topic

Sometimes referred to as clinical inquiry, formulating your research topic includes:

...asking the right questions in the right way, finding the best available evidence, and assessing what practice change may be needed...

From Wyant, T. (2018). A spirit of inquiry leads to evidence-based answers to practice questions. ONS Voice.

You can get started off right by first:

  • Gathering background information on your topic. Do a quick search to see what’s been written about the topic so far.
  • Considering your audience. Who will be interested in this issue?
  • Identifying a question framework to use to achieve clarity in the research question.
  • Soliciting input from collaborators, peers, and mentors.
  • Consulting with a librarian or information professional to assist you with a thorough search.

B: Brainstorm Search Terms

icon of letter bGenerating Search Terms (also known as Keywords)

Keywords are the words used in an article title, abstract, or other text field in a database. Keyword searching, or natural language searching, is how most people search for information and is often sufficient. One drawback of searching with keywords is that the words that you use must match the terms used by an author.

To remedy this problem, a complete keyword search strategy will include multiple spellings and synonyms that represent the concept. Keyword searching is also useful when attempting to identify literature that may not have been indexed with controlled vocabulary terms, for any variety of reasons.

Start by keeping a list in a document.

Keyword Generation Tips

  • See how publications and authors refer to your topic.
  • If looking for prevention, you will also need to look for causation.
  • Review MeSH or other database controlled vocabularies to find related terms.
  • Look at relevant articles on your topic to find potential keywords.
  • Browse a dictionary, thesaurus, or encyclopedia.
  • Think of synonyms, acronyms, antonyms, and initialisms associated with the concepts in your topic.

C: Choose Databases and Resources to Search

icon of letter cHow will you explain that you supported your topic with evidence? Surely not by saying "I Googled it!"

It is important to complete a thorough, documented literature search. Don't be afraid to call on the help of a librarian. A librarian can help you determine where to look and howto combine your chosen keywords for an efficient search.

There are some bibliographic literature databases that will have evidence in the form of clinical trials, systematic reviews, and more. Here are a few places you can try first:


PubMed is from the U.S. National Library of Medicine and the National Center for Biotechnology Information. It contains over 30 million records and includes the database MEDLINE. In PubMed, you will find clinical trials, systematic reviews, practice guidelines, meta-analyses, and more. Check out PubMed's Clinical Queries for pre-filtered searches for high-quality evidence.


CINAHL Plus contains reports of trials and studies in the Nursing and Allied Health professions.

TRIP Database

TRIP Database is a clinical search engine that will help you search in PICO format and point you to guidelines, trials, studies, and more.

Other Databases to Search

Browse our databases list by subject Meet with your librarian to determine relevant resources for your topic.

This short video demonstrates basic searching in PubMed and Trip Database and how to use the filters to limit to evidence.



D: Document Your Searches

icon of letter dWhy Document?

Documenting your search process will help you remember what you did and make your search transparent and reproducible.

Use a spreadsheet or document to capture:

  • Databases searched
  • Keywords used
  • Controlled Vocabulary used
  • Filters applied, such as language or date

In addition to the above type of documentation, you may also wish to use a citation management program, like Zotero or Mendeley. This will help you capture, store, and organize the sources you've chosen to read. It will also help you cite them later, by incorporating them into your manuscript or paper in the citation format of your choice.

E: Evaluate the Evidence

icon of letter e

Evaluate the Evidence: Reading a Research Paper

First, it's important to understand how to tackle the information that can be found in a research paper. This open access article from Carey et al. presents ten simple rules for understanding a research paper.

Carey, M. A., Steiner, K. L., & Petri, W. A., Jr (2020). Ten simple rules for reading a scientific paper. PLoS Computational Biology, 16(7), e1008032. DOI link:; PubMed Central Link:

This video, from Sketchy EBM, runs 4:17 and discusses what to focus on objectively when reading a research paper.

This short video runs approximately five minutes and demonstrates three checklists and one resource that can be used in the clinical appraisal of evidence.

Critical Appraisal and Evidence Grading

It is absolutely critical that you evaluate the evidence you've identified. Not all published research is without flaws. Fortunately, there are a handful of wonderful tools to help you appraise the evidence. To get started, see if these collections contain a checklist for the kind of study you've identified, and follow the prompts on the checklist:

It will be helpful for you to understand levels of evidence. Different kinds of evidence are better for answering different types of clinical questions. There are different iterations of evidence-based medicine pyramids or hierarchies.

University of Oxford Centre for Evidence-Based Medicine

Here is an example of evidence levels from the Centre for Evidence-Based Medicine at the University of Oxford for therapy / prevention, etiology / harm:

Level 1a Systematic Reviews (with homogeneity) of randomized controlled trials
Level 1b Individual Randomized Controlled Trials
Level 1c All or none randomized controlled trials
Level 2a Systematic Reviews (with homogeneity) of cohort studies
Level 2b Individual cohort studies
Level 2c "Outcomes" Research
Level 3a Systematic Reviews (with homogeneity) of case-control studies
Level 3b Individual case-control studies
Level 4 Case-series
Level 5 Expert opinion without explicit critical appraisal or based on bench research

Produced by Bob Phillips, Chris Ball, Dave Sackett, Doug Badenoch, Sharon Straus, Brian Haynes, Martin Dawes since November 1998. Updated by Jeremy Howick March 2009.

Johns Hopkins Nursing Evidence Based Practice Model

Here is an example of an abridged evidence-based medicine hierarchy from the Johns Hopkins Nursing Evidence Based Practice Model:

Level I Experimental studies, systematic reviews of randomized controlled trials
Level II Quasi-experimental studies, mixed methods, systematic reviews of randomized controlled trials and quasi-experimental studies
Level III Non-experimental studies, systematic reviews of randomized, quasi-, and non-experimental studies, mixed methods, qualitative meta-analysis
Level IV Expert opinions, clinical practice guidelines, position statements
Level V Traditional narrative literature reviews, quality improvement, case reports, opinions based on anecdotal evidence

Dang, D., & Dearholt, S. L. (2017). Johns Hopkins Nursing Evidence-Based Practice Third Edition. Indianapolis: Sigma Theta Tau International.