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Systematic Reviews

Conduct the Search

The goal of a systematic review evidence search is to identify all studies ​that contain data pertinent to the research question. ​​A comprehensive, transparent, and reproducible search of the literature is key to the validity of a systematic review's conclusions. 


Most searches begin with a core database. Even though databases can have overlap in their content, you should run your search in multiple databases to be as comprehensive as possible. Think about each of the components of your question and be open-minded about which databases might have what you are looking for. Searching a subject-specific database may yield results not found in more general databases.

Core Databases

Subject-Specific Databases

Developing a Search Strategy

Your database searches must be comprehensive and systematic. In order to retrieve the greatest number of relevant results, you need will need to conduct a broad, sensitive search, as opposed to a narrow, specific search. You will need to search all of the terms, synonyms, previous terms, subject headings, and ways of conceptualizing each of your question's components that you can. A broad search may return more results that do not meet your inclusion criteria, however it is important not to miss any eligible studies. 

How to Generate Search Terms


Use your PICO components.

In regards to each PICO concept, consider:

  • The definition - is it specific or vague? Consistent across time and/or people?
  • What different terms exist or have existed to refer to the same concept?
Scope out key articles on your concepts.
  • Read their abstracts and introductions.
  • Look at their lists of author keywords.
  • See if you can find the terms they were indexed with.
    • This is labeled differently in most databases. For example, it is "Publication Types, MeSH Terms, Substances" in PubMed and "Keywords Plus" in Web of Science.
  • Look at their references to find other articles.
Search databases' lists of subject headings.
  • Subject headings are terms that indexers use to identify the concepts of publications.
  • In EBSCOhost databases (like PsycIFNO), the searchable list of subject headings can be found under "Thesaurus" on the upper left of the page.
  • In PubMed, MeSH (Medical Subject Headings) is accessible in the dropdown box next to the search bar.
  • Pay attention to the definitions and level of specificity. Many terms have broader and narrower options that you can select from.

Note: the indexing process takes time and is not always immediately done for new articles, so do not rely solely on these terms.

Use the Yale MeSH Analyzer to discover more MeSH terms.
  • Find articles on your topic in PubMed.
  • Copy and paste their PMID numbers into the Yale MeSH Analyzer search box.
    • PMID numbers are listed on each search result near the bottom.
  • Select what information you want to view, and hit Go!
  • The table makes it easy to compare how articles have been indexed.

How to Modify Your Search With Boolean Operators:

  • OR - Broadens your search. The database will return any results with at least one of the terms. Use OR with words that are synonyms or have similar meanings.
    • Example: baby OR infant 
  • AND - Narrows your search. The database will only return results with both terms.
    • Example: infant AND leukemia
  • NOT - Narrows your search. The database will not return any results that contain the second term. Be careful using this operator (even for your exclusion criteria) because it could easily eliminate useful results.
    • Example: leukemia NOT lymphoblastic
  • (  ) - Parentheses can change the order in which operations are performed. Use them to organize your combination searches.
    • Example: (baby OR infant) AND leukemia vs. baby OR (infant AND leukemia)

Other search modifiers vary by database. Look for each database's Help or Tutorial pages to find more information. Here are some common modifiers:

  • * - Broadens your search. In many databases, an asterisk at the end of a word root will return results that include any word that begins with that root.
    • Example: infan* returns results that include infant, infants, infant's, infancy, infantile, infanticide, infantilize, infantry
  • ?- Broadens your search. In many databases, a question mark can be used to replace a letter in a word, and will return results with any letter in that position.
    • Example: wom?n returns results that include both woman and women


Be sure to document all aspects of your search, including the terms, Boolean operators, search fields, and punctuation you used in each database, and the date each search was conducted. The goal is to make the search fully reproducible.


Record Management

Your searches could potentially return a very large number of results, and you will want to keep a record of every single one of those, even the ones you end up excluding from your review! Using a citation management tool makes it easier to track and organize your search results throughout the review process. Importing results into one of these tools can help you to remove duplicates, screen for your criteria, access the publications, organize the results into folders, and format your citations, among other functions.

For more information about signing up for Covidence or linking your previous OSU or OSUMC affiliated Covidence accounts, please refer to our detailed graphic handout.

Citation Management Tools:

Tools designed specifically to help manage the systematic review process. Some have data extraction as well as citation management functions:

Grey Literature

An exhaustive search for a systematic review must look beyond traditionally published literature to find all relevant research and minimize publication bias. Materials produced outside of the traditional commercial/academic publishing and distribution channels by organizations such as governments, businesses, NPOs, professional associations, and health organizations are known as grey literature.

Examples of grey literature:

  • Technical or research reports
  • Theses and dissertations
  • Conference proceedings
  • White papers
  • Government reports
The following resources can get you started on your grey literature search. You may also need to search directly on the websites of relevant organizations to find grey literature:

Additional Ways to Find Studies

Even a well-developed database search strategy can leave gaps, thanks to limitations in each databases' scope and indexing. These additional methods can help you discover studies that your search may have missed. Be sure to document the methods your team uses and your results:

Reference Lists Scanning the reference lists of your results can help find relevant studies missed by your search.
Alerts for New Publications After creating profiles in databases, you can save your searches and set alerts for them so that you will be notified if anything new gets published. This is especially important if the topic of your review is a big focus in current research.
Citation Searching

Identify key articles you are including and search for other articles that have cited them.

Handsearching Identify key journals in your field that may or may not be included in the databases you chose and then manually scan their print or electronic contents for additional publications.
Contacting Experts Experts can be helpful in ensuring that you have found all of the relevant research. They can also be sources of information on unpublished or ongoing research.