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Systematical Search Strategies

Electronic databases are the primary tools for finding research literature.  The UH subject librarians could help you identify databases in your discipline. 

Keywords and Subject-Term are two main methods for conducting searches in databases. We recommend combining both methods to improve the thoroughness of your literature search.  To learn more about search strategies for systematic review, you may consult this series of Tutorials on Systematic Searches created by the librarians at the Yale University Medical Library. Here is a brief introduction of the two methods:

Keyword Search: 

  • keywords are the primary concepts in your research topic. 
  • Use "AND" to connect different concepts to get results that cover them all
  • Use quotation (" ") around phrases to ensure that the database searches for the exact phrase
  • Use synonym (or alternative words or phrases), and connect them with “OR” to retrieve more relevant results
    • Example: for the concept of "teenagers", the synonym could include "adolescent, adolescence, teens, teenager, juvenile" 
    • Scan relevant search results to discover new keywords and phrases that you could use
  • Use truncation mark to expand your search: When a truncation mark applied, the search would include various word endings and spellings. in EBSCO databases, an asterisk (*) is used to truncate a search word.
    • Example: aggre*   -- This will search for and find articles that contain the word aggressive, aggression, aggressiveness

Subject Term (Subject Heading) Search:

  • Subject terms are pre-determined "controlled vocabularies" used to describe the content of each article.
  • Subject terms are selected by indexers from a subject heading or term list and assigned to an article to help users to retrieve relevant articles. 
  • Each database has its own subject headings.  For example, Medline uses MeSH, Medical Subject Headings; PsycINFO, has a well-established thesaurus, and CINAHL has CINAHL Headings.
  • There are also databases that don't have a subject heading,. Scopus and Web of Sciences are examples.  You can only use keywords search for those databases.
  • Please contact your subject librarian for more information about subject heading searches.

What is grey literature?

Grey literature is often referring to literature that is not obtainable through normal publishing channels, or research published outside of commercial or academic publishing. It could include:

  • Reports from government agencies
  • Conference proceedings
  • Pre-prints and post-prints of articles
  • Theses and dissertations
  • Policy statements 
  • Research reports and working papers from think tanks, companies, and research institutes

How to find grey literature?

  • Identify key relevant authorities and organizations and use Google's advance search feature to explore their websites
  • Search existing databases for the above types of materials.


The citation tracking or snowballing method: This method allows you to widen your search by taking advantage of the references cited in a relevant article.  There are two approaches to this.  First, you can scour the reference sections of articles that you have already included in the review and pick up the ones that could be added to your list.   Second, you can use certain citation tracking databases (i.e., Scopus and Web of Science) to identify articles that had subsequently cited papers that you have included in the review.  The first approach works back in time from the article (backward tracking), whilst the second approach works forward in time from that article (forward tracking). 

Hand searching: Handsearching is manually searching for articles or reports in selected journals, reports, or other types of relevant publications.  This method would help identify articles missed from the electronic database searches due to insufficient database indexing or errors. It is a process of searching journal contents or reports page by page, cover to cover to identify the relevant studies. 

Contact experts in the field could help you identify other or on-going studies they may be aware of but have missed by other literature search methods.  This is a highly recommended step by serval organizations that support evidence-based research.  As Petticrew & Roberts (2006) suggested in their book, Systematic Review in the Social Sciences, "Even if no additional studies are turned up by the experts, you will have greater confidence that you have identified all the relevant studies, and it also offers an opportunity to let other experts know that the review is underway."