Systematic Literature Reviews

Effective searching creates the foundation for your systematic review.

Your aim is to maximize precision (the number of relevant sources found by your search divided by the total number of sources found by your search) without sacrificing recall (the number of relevant sources found by your search divided by the total number of existing relevant sources). 

The Covidence Academy's "How to write a search strategy for your systematic review" is a good starting resource for writing effective searches.

As you begin your project, it is important to define a clear scope of your review. Craft your research question. Brainstorm the inclusion and exclusion criteria that you will use to screen sources. Start to identify search terms related to your question and criteria.

Inclusion and exclusion criteria are developed after a research question is finalized but before a search is carried out. They determine the limits for the evidence synthesis and are typically reported in the methods section of the publication. 

Examples

• Date: If there has been a previous review undertaken, then it is not necessary to go back over ground covered in the earlier review. Instead, refer to it and the findings from that study in your introduction,
• Exposure of Interest: The participants in the study may need to have experienced a particular condition to be considered for inclusion (e.g. received prenatal classes, given a particular drug, had a disease at a particular graded level or higher).
• Geographic location of study: It may be necessary to limit the review to only studies targeting the same population group of interest for a broader original study or to countries which share similar demographic or economic factors with the target group.
• Language: It is usually not necessary to arrange translation of scientific works unless the review is attempting to come to a definite conclusion about a very specific clinical outcome which requires every applicable paper to be included.
• Participants: Reviews may be restricted to only adults, children, or certain age groups. Some databases include age group filters that can limit results to your target group.
• Peer Review: Sometimes reviews will exclude non-peer reviewed literature but gray literature such as technical reports and web-based guidelines may be important for certain research questions.
• Reported Outcomes: The inclusion of a study may depend on whether particular outcomes of interest have been reported in an appropriate, consistent manner. For example, outcomes may be excluded if they are self-reported.
• Setting: The study may be excluded or included based on where the participants were located (e.g. school, hospital, inpatient, community-based care).
• Study Design: The inclusion of only selected study designs is a way to make the review much more manageable and applicable to the research question. Study designs can include those in which participants were surveyed at one point in time (e.g. cross-sectional studies and ecological studies) and study designs that are conducted over time.
• Type of Publication: Systematic reviews usually search for original studies. Commonly excluded publications are reviews and editorials. Letters may also be excluded, however, this should be done with caution as sometimes the letter format will be used to report small-scale studies.

The PRISMA Flow Chart is a helpful way to track and report inclusion/exclusion decisions. An in-depth explanation of the PRISMA guidelines can be found in "What is PRISMA guidelines & what's new in the 2020 update" by Covidence Academy.

Identify Search Terms

You will most likely add search terms as you dig into the databases and available research. One way to keep track of your keywords is to create a simple table like the following:

Each time you identify an additional synonym for a concept, add it to the appropriate set of keywords. Notice that each set is being built with "or" separating each word. This makes it easier to translate it into the database search later. 

In this example, multiple-word phrases are encased with double quotation marks. This is a common way to make sure databases search for full phrases rather than individual words.

You might also decide to truncate words that would have multiple endings. This is often signified with an asterisk (e.g., injur* would retrieve injury, injuries, etc.). Because databases have their own search functions and algorithms, it is best to examine what works for each one.  

Additional Tips for Identifying Search Terms

• Run a search for each concept individually in one or more databases. Look for articles relevant to your concept or research question. Look for new words or variations from titles, abstracts, author keywords, and subject lists. 
• Use subject-specific lists of vocabulary like MeSH (Medical Subject Headings) or ERIC (Education Resources Information Center).
• Ask a librarian to help you identify additional search terms.

If relevant, use the concepts from the PICO (Population, Intervention, Comparison, Outcome) or SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type) frameworks to develop sets of keywords.