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 Merriam-Webster.com. https://www.merriam-webster.com/dictionary/.
…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. https://doi.org/10.1136/bmj.312.7023.71.
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 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. https://dx.doi.org/10.5195%2Fjmla.2020.803.
The framework below uses ABCDE to guide you through the searching process.
Assess Your Topic, Scope, and GoalsAssess 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.
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. https://voice.ons.org/news-and-views/a-spirit-of-inquiry-leads-to-evidence-based-answers-to-practice-questions.
You can get started off right by first:
Generating 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.
How 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 is a clinical search engine that will help you search in PICO format and point you to guidelines, trials, studies, and more.
Browse our databases list by subject Meet with your librarian to determine relevant resources for your topic.
Why 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:
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.
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: https://doi.org/10.1371/journal.pcbi.1008032; PubMed Central Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7392212/
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.
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. https://www.cebm.net/2009/06/oxford-centre-evidence-based-medicine-levels-evidence-march-2009/
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. https://www.worldcat.org/title/johns-hopkins-nursing-evidence-based-practice-model-and-guidelines/oclc/1001413926.
