As mentioned in Step 1, it's a good idea to do some rough preliminary searching before you start your systematic approach. This will help with identifying key authors and keywords and come up with a very few articles which seem important to your topic. These key articles will become your "gold set" which you can not only use to identify search terms, but down the track can help you test your final search strategy. If these articles don't come up when you test your strategy in the databases, you must be missing something.

You can also use your gold set for snowball searching ​- following links to citations and reference lists of an article to find related articles.

Back in Step 1, you formulated your research question and may have used a search framework to help you do this. The framework (and the question itself) will direct you to the main two or three concepts you need to search. For each concept you will need to consider all the different terms that could be used to describe it. Your knowledge of the topic along with any preliminary searching you have done will help you identify the specific search terms to use.

Think of as many terms and synonyms for each concept as you can, including:

• both scientific and common terminology
• alternative spellings (such as British and American spellings, and possibly common misspellings)
• outdated and culturally-specific terms
• abbreviations or acronyms
• plurals
• database-specific controlled vocabulary or thesauri (eg. MeSH in Medline, CINAHL Headings in CINAHL)

For example, using the scenario we described earlier, “Does cranberry juice help reduce urinary tract infections in people living in aged care facilities?”

Once you've come up with as many specific terms as you can find, each concept will be linked with the AND operator in the final search strategy. 

Usually you would not include every framework element in your search strategy. Here we have left out the Comparison element as there is no clear comparative intervention. Often the Outcome is left out because it comes out of all the found studies in any case, and may restrict the scope of the search.

It's important for any literature search to consider the limitations of your search. For systematic reviews it is vital that you establish the boundaries  very early on. Which studies will be excluded from the review and why? 

For a systematic review, information about the inclusion and exclusion criteria is usually recorded as a paragraph or table in the methods section.

Common criteria include:

• Time period - Perhaps there has been a previous review and this is an update, so included articles may be only those published since the previous review.
• Language - It is not usually necessary to arrange for translations of articles published only in other languages.
• Publication type - Usually you will only be looking for original studies, so you may consider excluding editorials and letters.
• Geography or setting - You may need to limit the review to a particular population group, or a particular setting (eg. school or hospital).
• Age groups - Many databases include particular age groups as subject headings or limits if this is relevant to your research question.
• Study design - Consider including specific study designs, such as controlled trials or qualitative studies, if that is applicable to your question. This could be a way of making a broad review more manageable.