Searching Best Practices for Evidence Synthesis Reviews

Limiters are database features that you can check to instantly limit your results. Common limiters include language, date range, full-text, and publication type. The issue with limiters in a systematic review is twofold:

• Limiters rely on indexing. (See Utilize controlled vocabularies and keywords section) The newest articles in a database will not be indexed immediately. Some articles in a database will never be indexed. Indexing is also not perfect and can sometimes include mistakes (e.g a study being marked as an RCT when it is not an RCT).
• With a click of a button, you will be removing a significant amount of articles from your search results. You will have no idea what you are removing and if there are some articles that actually may have been relevant to your review.

Avoid using database limiters at all during your evidence synthesis review. With a quality search and your critical appraisal process, you shouldn’t need to rely on limiters to sort through your results for you.

Published (or sometimes called validated) search hedges or filters are search strings that can be used to narrow your search to certain criteria to retrieve relevant articles. These search strings have been tested to ensure that they are the most accurate as possible at returning relevant results. Search hedges/filters are different from database limiters because they are actually search strings rather than buttons you can click inside the database. The creators of these search strings then can publish these hedges in articles or on websites. Common criteria for hedges include:

• Age
• Gender
• Type of study (like RCTs)
• Animal or Human studies

While there are common search hedges, you can always check to see if a search hedge has been created for a specific concept in your research (for example, PubMed has search filters for health disparities as well as COVID-19). Three very important things to remember with search hedges:

• Pay attention to when the search hedge was published. Databases change their syntax and subject headings frequently so a search hedge can quickly become out of date. Always make sure to check if the syntax and headings are current.
• Check to see what database the hedge was developed for. Search hedges will need to be translated to each database just like any other search string.
• If you use a search hedge that was created by someone else, you will need to cite it.

You can always use a search hedge as a jumping off point to help you create your search strategy or to make sure your search strategy is on the right track.