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Systematic Review: How to Search

This guide presents tools and advice for conducting systematic reviews.


PICO (Population, Intervention, Comparison, Outcome) is a commonly used tool for formulating focused clinical questions. You can use to PICO to clarify your question, determine search concepts and the type of study that is most appropriate to answer the question type.


Use PICO to determine your search terms and also think about synonyms, abbreviations and spelling variants which might be used by authors.

Check to see if your database uses controlled vocabulary, i.e. MeSH in Medline and check your search terms to see if they have a corresponding control term and add them to your search strategy. You will need to use both keywords and controlled vocabulary to be complete when searching.

N.B. Different databases have their own controlled vocabulary, which means that you will need to remap your terms as you switch between databases.

Document your search strategy as you develop it. This will prevent confusion when you start searching.

Use database accounts to save and run your searches. This will also allow you rerun your searches at a later stage.

Get more information on developing your search strategy from the following guides:

Cochrane Handbook

Chapter 6 Searching for Studies gives good advice on formulating a search strategy

Searching for studies: A guide to information retrieval for Campbell Systematic Reviews

Appendix 2: Example search strategy to identify studies from electronic databases gives an overview of the process

Using Search Filters

What are Search Filters?

Search filters are pre-formulated search strategies that can be used to refine your searches in order to find certain kinds of results. You can use them to refine your search by such criteria as study design, age, gender among others.

Search filters are designed for specific databases and interfaces, so make sure that you have the appropriate filter for your search. They are being continually being rerfined and improved, so make sure that you pick the most up to date version.

Using  a search filter

Once you have located your filter, you can run it in your database. Each line of the search filter is a separate search on teh database and must be implemented exactly as is laid out in the search filter. Once your have finished you can then "AND" it with you your original search strategy to get your results.

Top Tip: You can save time by saving your search filter from the database search history and then just rerunning it when ever you need to.

Examples of Search Filters

Where to Search for Primary Studies

Selecting sources to search

The sources you decide to search will depend on your discipline. Here is an initial selection of databases that you might find useful for your systematic review. You can find a more complete of databases by discipline here.

Sources for Health

Sources for Human Sciences

Grey Literature


Handsearching journals and conference proceedings can be a useful adjunct to searching electronic databases for at least two reasons: (1) not all trial reports are included in electronic bibliographic databases, and (2) even when they are included, they may not contain relevant search terms in the titles or abstracts or be indexed with terms that allow them to be easily identified as trials