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Systematic Reviews

Design your Search

Search Strategy

The aim of the search strategy is to maximise the retrieval of relevant documents and minimise the retrieval of irrelevant material. It is necessary to strike a balance between achieving comprehensiveness and maintaining relevance when developing a search strategy.

Inappropriate/ inadequate search strategies may fail to identify records that may affect the comprehensiveness of your review.  Below are some of the pointers for building a simple and effective search. 


PICO is used to formulate a search statement. It is not necessary to include all of the PICO concepts in the search strategy.

Although a research question may address particular populations, settings or outcomes, these concepts may not be well described in the title or abstract of an article or indexed with the controlled vocabulary terms.  For a basic search, it is preferably to search for concepts that can be clearly defined and translated into search terms.

2. Search tips

Boolean logic ( "AND" "OR" and "NOT") is used to express the relationships between search terms.

3. Restrictions
Restrictions are not advisable for:

  • Language - all relevant studies should be included regardless of language.   
  • Date - Limit your search by appropriate date only if the availble literature is published after certain time period.  For example, Covid-19 literature only available since the end of 2019, you can use the date limit to restrict search from 2019 onwards.

4. Revising your search strategy

Search strategy should be revised when

  • No relevant articles are retrieved from the databases
  • Some key articles are found to be missing from the search 
  • New concepts or additional search terms that can be used to retrieve further studies  ​

​​5. When to stop searching

Generally, if your search strategy has no longer retrieved new studies or relevant articles, this means your search has reached the saturation point.  The call to abort searching further depends on the significance of the research question, the purpose of the review and the resources that are available.  

PRESS - Peer Review of Electronic Search Strategies

An Evidence Based Checklist for the Peer Review of Electronic Search Strategies (PRESS EBC)  is available here.

Here are some factors to consider when constructing your search statements (adapted from PRESS):


  • Is the search question translated well into search concepts?


  • Are there any mistakes in the use of Boolean or proximity operators?

Subject headings

  • Are any important subject headings missing?
  • Have any irrelevant ones been included?

Natural language

  • Are any natural language terms or spelling variant missing?
  • Have any irrelevant ones been included?
  • Is truncation used optimally?

Spelling & syntax

  • Does the search strategy have any spelling mistakes, system syntax errors, or wrong line numbers?


  • Do any of the limits used seem unwarranted?
  • Are any potentially helpful limits missing?

Database adaptations

  • Has the search strategy been adapted for each database to be searched?