In order to cover your bases, you'll want to have (and document) a thorough search strategy that includes:
Databases and indexes
Reference lists (of existing systematic reviews & studies chosen for inclusion)
Contacting authors, organizations, conferences
Grey literature sources, which may include preprints, dissertations, registered trials, conference proceedings, and periodicals.
There are 3 main types of searches:
Generally speaking, exploratory searching is where you start. This includes searching for existing reviews and getting a rough idea of the scope of the literature. It is also a way for you to test your search strategy and individual terms before conducting the systematic search. Exploratory searching should guide you in developing your research question and eligibility criteria as well as developing your search strategy. We highly recommend reaching out to a librarian for help with exploratory searching.
The systematic search is what you will document in the methods section of your paper. Once you have finalized your search strategy, you will implement that search in each of your chosen databases individually. The more rigorous guidelines expect you to document your search, the number of search results per database, and the date on which the search was conducted.
Hand or supplementary searching picks up articles that may be missed in your systematic search and will occur concurrently with exploratory and systematic searching as well as through the screening stage. This type of search includes directly searching highly relevant journals that may not be indexed in your chosen databases as well as recently published articles in journals that are indexed but may not show up in the databases yet. It also includes looking at research that does not appear in academic journals, like clinical trials, dissertations, and other gray literature. Once you have determined the articles you will use in your review, you should comb through their reference lists to pick up any citations your own searches may have missed.
Best practice for systematic searching recommends searching at least 3 databases including one that is multi-disciplinary.
To help you determine which databases will be best bets for your research questions, you can ask a librarian, but you'll also want to look at existing reviews that ask similar questions to your research question and likely you will want to use a similar list of databases to the ones they report.
Identify and test your search terms in your identified databases before conducting your final structured search.
To cover biomedical or medical literature, you will want to select a version of the PubMed/MEDLINE database.
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