Once you have defined your focused research question, and determined your inclusion and exclusion criteria, you now need to develop your search strategy to ensure all relevant literature is retrieved from a variety of sources.

In designing your search of the literature, you should consider:

• gathering a 'sample set' of references
• having a comprehensive list of search terms
• doing a 'test run' of your search queries
• revising your search strategy (if needed)
• identifying which sources to search - databases, grey literature

It is useful to build a 'sample set' of relevant references before you develop your search strategy.

The 'sample set' of references will enable you to:

• help identify relevant search terms
• test that your search strategy will retrieve these references (and subsequently other relevant references on your research topic)

The 'sample set' may include:

• key papers recommended by your supervisor
• using known relevant articles to identify other key articles
• references used in similar systematic reviews
• results of preliminary 'scoping searches' from key databases

The search strategy needs to include a detailed list of search terms for each concept to ensure all relevant studies are captured for the review. Search terms will be made up of keywords, or phrases, as well as database subject headings. Each database uses a different criteria to classify articles, so the subject headings will differ between each one.

To assist in identifying useful search terms:

• Dictionaries/thesauri will provide synonyms
• Check your 'sample set' -
  • look for keywords that the author may have provided
  • look for keywords and phrases used in the title/abstract of the papers
  • if you have systematic review papers these may include their search strategy
• Search for subject headings from databases

You also need to consider the limits you intend to apply to your search. Searches of databases will provide options that include:

• Language: Should you restrict to English language publications only?
• Species: Humans? Animal studies?
• Gender: Are you focusing on males or females?
• Age: Are you focusing on a particular age group?
• Study/publication type: Are you restricting your search by publication or study type? Systematic review or meta analysis, randomized controlled trial?
• Time period: Will your review be restricted by year of publication? Or is it important that you cover all years?

When using multiple databases you are likely to encounter a large volume of resources. During the search stage, you can continually adjust research questions, search terms and/or selection criteria in order to make sure you have a comprehensive body of references.

It is recommended that you test your search terms to determine if all the subject headings and words/phrases will return useful results. Test your search strategy in a key database. Does it retrieve any papers from your 'sample set' that are contained in that database? Are the results of the search relevant to your topic?  What proportion are irrelevant? Identify any terms that are retrieving large numbers of irrelevant papers.

Now that you have completed the preparation for your systematic review, it is time to execute your search and analyse search results to determine the papers that will be included in your review.

It is essential that you thoroughly document your search process in enough detail to ensure that it can be reported correctly in the review. You may choose to create a spreadsheet to record the details of your searches, and to save your search histories - this requires setting up a free personal account in each database.

For each database search you conduct, you should record:

• the date the search was run
• the name of the database
• the name of the database provider (e.g. ProQuest or EBSCO)
• your search strategy - include the keywords you used and how these were combined in the search
• the years searched
• any filters or limitations used, such as date, language, etc.
• the number of studies identified