Minimizing bias in locating, selecting, coding and aggregating individual studies for a systematic review is essential. A source selection bias may result if a range of sources are not searched to capture all relevant material.
A systematic approach to searching the literature for Systematic Reviews will help to identify all of the best available literature that addresses your specifc clinical question.
Checking existing reviews/protocols ensures that you are not repeating someone else's work and that you are not wasting resources. It is always necessary to check whether a systematic review answering your question has already been conducted or is currently being undertaken. This may help you in choosing or refining a review topic. Look for existing reviews/protocols in:
Alerts are an effective means of keeping track of the latest research. Many databases and journals offer free alert services through emails and RSS feeds. Types of alerts include:
When you have constructed your systematic search you can sign into the database (create an account) which allows you to save searches and also to create them as alerts so you are notified when new articles which match your search are added to the database.
Key databases - Search appropriate national, regional and subject specific bibliographic databases. Medline and Embase are examples of key databases. Subject specific databases, such as PsycINFO or CINAHL, relevant to the review topic should also be covered.
Reference lists in any included studies and any relevant system reviews must be identified.
Trial Registers and repositories of results - Many of the clinical trial registers include information about trials that are in progress as well as those that have been completed. Examples include:
Other reviews and guidelines - Some useful examples are:
Hand searching involves examining manually key journals, conference proceedings and other relevant publications page by page. Hand searching is to overcome deficiences in indexing or database coverage. Conference proceedings are important to hand search because inidividual conference papers are rarely indexed.
Grey literature sources include reports, dissertations, theses etc. For more information click on the grey literature tab.
Citation indexes such as Web of Science and Scopus allow you to track literature over a period of time.
Individuals and organisations - relevant personnel and associations/societies/groups should be identified and tracked down for information about unpublished or ongoing studies for possible inclusion in reviews.
Internet - An Internet search can identify websites of relevant organisations, companies, academic centres which can then be scanned for relevant research studies. It may be worthwhile to try more than one search engine as you can often get different results from different search engines even when using the same search.