Searching is a critical part of the systematic review. Before you start typing keywords into a database to run a search straightaway, it is crucial to plan your search strategy first. This process enables you to:
Steps to develop a search strategy:
* Not all elements of a research question or from the PICO should necessarily be used in the search strategy. Some elements are less important than others. Adding an element to a search strategy increases the chance of missing relevant search results.
Depending on your review question, you need to identify relevant databases to search in your review. The goal is to ensure your search is comprehensive.
Below are some of the key databases in Medicine and Health Sciences. Click here for the full list of databases.
What is Grey Literature?
Grey literature refers to materials and documents not controlled by commercial publishers and it is usually not discoverable in databases, making it difficult to search for and retrieve. Grey literature is produced by the government, academia and industry.
Grey Literature is also defined as:
"Information produced on all levels of government, academia, business and industry in electronic and print formats not controlled by commercial publishing i.e. where publishing is not the primary activity of the producing body." Source: ICGL Luxembourg definition, 1997, Expanded in New York, 2004
Searches for studies should be as extensive as possible in order to reduce the risk of publication bias. It is highly desirable to search relevant grey literature sources such as reports, dissertations, theses, databases and conference abstracts/papers. (Source: MECIR Manual C28)
Examples of grey literature include:
More examples of grey literature: GreyNet International - Document types in Grey Literature
Key sources for Theses and Dissertations:
Click here for more databases on Dissertations and Theses.
Key sources for Conference Abstracts & Proceedings:
Some library databases also include conference papers:
Search Tips: To limit search results to conference papers, look for the filters or limits on “Publication Type”, “Content Type”, or “Article Type” and select "meeting/conference abstracts", "proceedings paper", or "conference papers".
Many clinical trials are in progress, grey or unpublished. It's important to include searching unpublished and ongoing studies in your SR to minimise bias.
Source: Cochrane Handbook, 4.3.3
Key sources for Trials Registers:
According to Cochrane Handbook, 4.3.3, "Research has shown that even though ClinicalTrials.gov is included in the WHO ICTRP Search Portal, not all ClinicalTrials.gov records could be successfully retrieved via searches of the ICTRP Search Portal." Therefore, you may also want to search individual trial registers.