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Systematic searching: 8. Limiting the search

Limiting the search

Many databases provide different filter tools that allow you to limit your search results. The most common filter tools for limiting search results are publication language, year of publication, and peer-review. Other filters may include, depending on the database, e.g. age group or publication type. 

Keep in mind, however, that limiting your search results with filter tools should only be used with caution when undertaking a search for a systematic review since they may remove relevant documents from your search results. Filter tools may also eliminate the most recent documents from your search results if they have not yet been fully indexed into the database. The reporting and reproducibility of the search strategy also suffers from the use of filter tools, as the database algorithms are not transparent, i.e. we do not know for certain exactly how the search engine functions.  

NOTE. In a systematic review, all search limiters must be both defined before the search is undertaken as well as described in the protocol. You also need to be consistent when applying search limiters. 

Set strings of keywords 

In systematic searching it is often better to use set strings of keywords, also called search filters or hedges, i.e. sets of keywords to describe an aspect, to limit the search rather than the database's own filter tools. You can find ready-made collections of search filters for different purposes below: