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Systematic Reviews

Tips to search for more keywords

After identify the key concepts from your focused research question, here are some of the tips to brainstorm for keywords:

1. Conduct a preliminary search on the topic

Based on the key concepts “sleep disturbance” AND dementia, run a preliminary search to discover keywords used by authors to describe the concepts in titles, abstracts or author's keywords in databases.

2. Look for existing review on your topic

During the preliminary search, you can use the built-in systematic reviews filter or type a search term “Systematic Review” to find similar systematic reviews which will provide useful hints on the search strategy and and whether your search terms are sufficient for the research topic.

3. Search for primary studies/core articles for the topic:

Based on one or a few key papers, you can look at the reference list as well as the citing articles of the paper to find more relevant articles.  This method is known as snowballing or pearl growing which allow searchers to conduct a backward/forward citation searching/referencing.

4. Make use of controlled vocabulary (index term or subject headings):

  • Most of the bibliographic databases such as PubMed, Embase, PyscInfo provide controlled vocabulary. You can use it to find a suitable subject heading such as Mesh term in MEDLINE or Emtree term in Embase to refine your search strategy.
    • For example, when searching the MeSH Database, you can check their Entry terms, Used for terms, Related terms that describe the same concept.
    • You should also check for narrower terms as well as the broader term in the subject hierarchy. This might give you clues on the relationship of these similar terms to help you decide on the most suitable subject heading to be included in your search.
  • Do note that controlled vocabulary can be searched as keywords.

5. Others

After identifying all the keywords, it is time to combine them using Boolean Operators and apply basic searching techniques such as truncation, phrase searching and parentheses to build a search startegy to retrieve relevant articles.

Boolean Operators

Using the "AND" Operator to combine different concepts to narrow the search results.

Using the "OR" Operator to combine synonyms/alternative terms to broaden the search results.

Using the "NOT" Operator to remove concept. Avoid using this as it might remove relevant results. You may use this to fine-tune the results.

Phrase Search, Truncation and Parentheses (aka Nesting)

Truncation - retrieves records with spelling variants containing a common root word. The symbol for truncation is usually an asterisk (*).

Caution: It may retrieve many irrelevant results if the root word is too short or common. For example, app* for apps, application, apple, apply etc.  Do note that PubMed only searches root word with a minimum of 4 characters.

Phrase Searching - retrieves records with the exact phrase. Use quotation marks (" ") around the phrase that you need to find.

Caution: Searching using Phrase Searching technique will limit the number of studies. For example, searching "risk taking behavior" will miss out article using "risk taking behaviors" as well as "risk taking behaviour"


Parentheses (aka Nesting or Brackets)- to enclose a set of search terms especially a set of synonyms/alternative terms with Boolean Operator OR so that the database will proceed with the search for the first enclosed first.

Caution: Too many/Incomplete parentheses will cause error in searching especially for keywords search databases such as Scopus and Web of Science.