Working with a librarian during this phase is highly recommended. Librarians bring expertise in database functionality, controlled vocabularies, and advanced search construction—all critical for designing effective, reproducible search strategies.
A key step in conducting a systematic review is selecting the right databases. Because no single database covers all disciplines or sources, using multiple databases is essential to capture the full scope of relevant literature and reduce selection bias. Each database has its own structure, features, and search syntax. To manage this complexity, we recommend creating a single master search strategy that reflects your core concepts, then adapting it to meet the requirements of each database.
Grey (gray) literature refers to materials produced outside of traditional academic or commercial publishing, such as government reports, dissertations, theses, white papers, working papers, and conference proceedings. These resources are often not indexed in major bibliographic databases, which can make them more difficult to discover—but they are no less essential to a comprehensive evidence synthesis.
Why include grey literature? Scientific publishing tends to favor studies with statistically significant results, leaving many null or inconclusive findings unpublished. This creates publication bias, which can distort the conclusions of your review. By searching for grey literature, you help ensure that all relevant evidence—published or not—is considered. Including grey literature in your review increases transparency, reduces bias, and helps ensure your conclusions are based on the fullest possible body of evidence.
Tips on finding grey literature: To get started, check existing reviews or protocols on similar topics to see what grey literature was incorporated in their study. Don't hesitate to reach out to colleagues or researchers in your field about unpublished studies or useful grey literature repositories. Visit websites of professional associations, government agencies, and research institutes related to your topic.
Tool for Finding Grey Literature:
Theses and Dissertation:
Publication Dates Covered: 1861 - present; full text varies by school Paid for by K-State Libraries
Includes full text for many dissertations written after 1996, including some master’s theses. Copies of dissertations not available in full text in this database may be requested via interlibrary loan and/or purchased as microfilm or as unbound copies from UMI. You can limit the search to K-State dissertations only. Also, this database can be searched in the Web of Science (includes all databases) platform.
Preprint Repositories:
A strong search strategy helps ensure that your review is comprehensive, reproducible, and transparent—and that you don’t overlook relevant studies. The goal is to capture all relevant evidence. It’s highly recommended to work with a librarian to develop a search strategy across multiple databases while making strategic use of controlled vocabulary, database-specific syntax, and Boolean logic.
Boolean operators combine search terms to broaden or narrow your search:
AND narrows (e.g., children AND obesity)
OR broadens (e.g., (children OR adolescents))
NOT excludes (e.g., obesity NOT diabetes)
Database search techniques:
These techniques can be database-specific. Be sure to check with your librarian or the help section of the selected database to be sure they will work with your search:
Use quotation marks to search exact phrases: “child development”
Use truncation symbols (usually *) to find word variations: educat* retrieves educate, education, educational, etc.
Use parentheses to group terms and control the search order: (child OR adolescen*) AND (exercise OR "physical activity")
Controlled Vocabulary
Many databases use subject headings or controlled vocabulary—standardized terms used to tag articles on the same topic. For example, in PubMed, the controlled vocabulary is called MeSH (Medical Subject Headings). Use both controlled vocabulary and free-text terms in your strategy to maximize your results.
Thesaurus
Similar to a controlled vocabulary, a thesaurus can identify standardized terms used to describe articles found within the database. Typically, definitions of the terms will be provided. Also, opportunities to broaden or narrow the term are available.
Field-Specific Searching
Focus on fields like title, abstract, and keywords, rather than full text, to maintain transparency and reproducibility. Searching full text can increase the results and create more false positives. This will increase the screening time for your evidence synthesis project.
Resources for Search Strategies:
When conducting evidence synthesis or systematic reviews, it's essential to understand that databases differ in search interfaces, syntax, and platform-specific rules. While your overall search strategy—built around core concepts and keywords—remains consistent, each database requires a customized translation to ensure the search functions correctly and retrieves accurate results.
For healthcare-related searches, consider using the Systematic Review Accelerator-Polyglot. Polyglot will translate search strings across different databases to help save you time in creating multiple search strategies. You will still need to understand how the other databases work.
Export Searches: After translating your search strategies and running them in each database, export your results in a standardized format (e.g., .RIS, .XML, BibTeX, or .MEDLINE). Be aware of export limits from different databases.
Import into a Citation Manager program (i.e., Zotero, EndNote) and double-check that the number of citations imported matches your final search results.
As you execute your searches, document the following for each database:
