The content in the Literature Review section defines the literature review purpose and process, explains using the PICO format to ask a clear research question, and demonstrates how to evaluate and modify search results to improve the accuracy of the retrieval.
What is a Literature Review?
A literature review seeks to identify, analyze and summarize the published research literature about a specific topic. Literature reviews are assigned as course projects; included as the introductory part of master's and PhD theses; and are conducted before undertaking any new scientific research project.
The purpose of a literature review is to establish what is currently known about a specific topic and to evaluate the strength of the evidence upon which that knowledge is based. A review of a clinical topic may identify implications for clinical practice. Literature reviews also identify areas of a topic that need further research.
A systematic review is a literature review that follows a rigorous process to find all of the research conducted on a topic and then critically appraises the research methods of the highest quality reports. These reviews track and report their search and appraisal methods in addition to providing a summary of the knowledge established by the appraised research.
Obviously, the quality of the search process will determine the quality of all literature reviews. Anyone undertaking a literature review on a new topic would benefit from meeting with a librarian to discuss search strategies. A consultaiton with a librarian is strongly recommended for anyone undertaking a systematic review.
Use the email form on our Ask a Librarian page to arrange a meeting with a librarian.
Clearly Stated Research Question
The first step to a successful literature review search is to state your research question as clearly as possible.
It is important to:
be as specific as possible
include all aspects of your question
Clinical and social science questions often have these aspects:
Comparisons (not always included)
If the PICO model does not fit your question, try to use other ways to help be sure to articulate all parts of your question. Perhaps asking yourself Who, What, Why, How will help.
Example Question: Do electric toothbrushes work as well as or better than manual toothbrushes to remove plaque when used by children?
Note that this question fits the PICO model.
Intervention: Electric toothbrush
Comparison: Manual toothbrush
Outcome: Plaque removal
A literature review search is an iterative process. Your goal is to find all of the articles that are pertinent to your subject. Successful searching requires you to think about the complexity of language. You need to match the words you use in your search to the words used by article authors and database indexers. A thorough PubMed search must identify the author words likely to be in the title and abstract or the indexer's selected MeSH (Medical Subject Heading) Terms.
Start by doing a preliminary search using the words from the key parts of your research question.
Step #1: Initial Search
Enter the key concepts from your research question combined with the Boolean operator AND. PubMed does automatically combine your terms with AND. However, it can be easier to modify your search if you start by including the Boolean operators.
children AND electric toothbrush AND manual toothbrush AND plaque removal
The search retrieves a number of relevant article records, but probably not everything on the topic.
Step #2: Evaluate Results
Use the Summary drop down in the upper left hand corner of the results page to change the display to show all the Abstracts.
Review the results and move articles that are directly related to your topic to the Clipboard.
Go to the Clipboard to examine the language in the articles that are directly related to your topic.
look for words in the titles and abstracts of these pertinent articles that differ from the words you used
look for relevant MeSH terms in the list linked at the bottom of each article
The following two articles were selected from the search results and placed on the Clipboard.
Mascarenhas AK, Soparkar P, Al-Mutawaa S, Udani TM. Plaque removal using a battery-powered toothbrush compared to a manual toothbrush. J Clin Dent. 2005;16(1):23-5. PubMed PMID: 15974220.
Silverman J, Rosivack RG, Matheson PB, Houpt MI. Comparison of powered and manual toothbrushes for plaque removal by 4- to 5-year-old children. Pediatr Dent. 2004 May-Jun;26(3):225-30. PubMed PMID: 15185803.
Here are word differences to consider:
Initial search used Children. MeSH Terms use Child.
Initial search used Electric Toothbrush. Article titles use Battery-Powered, Powered. Related word from MeSH Terms is Electricity.
Initial search used Manual Toothbrush. Article title uses Manual Toothbrushes. Related word from MeSH is Toothbrushing.
Initial search used Plaque Removal. Article titles use this exact phrase. MeSH Terms use Dental Plaque combined with Therapy, Prevention, Control.
With this knowledge you can reformulate your search to expand your retrieval, adding synonyms for all concepts except for manual and plaque.
#3 Revise Search
Use the Boolean OR operator to group synonyms together and use parentheses around the OR groups so they will be searched properly. See the image below to review the difference between Boolean OR / Boolean AND.
Here is what the new search looks like:
(child OR children) AND (electric OR electricity OR battery OR power OR powered) AND manual AND (toothbrush OR toothbrushes OR toothbrushing) AND plaque AND (removal OR remove OR therapy OR prevention OR control)