Searching the literature: bibliographic databases and grey literature
Once you have defined your search concepts and thought about your search terms, you can begin searching for your systematic review. We suggest you start your search by using relevant subject databases and then consider adding other searching approaches such as following a citation trail or extending your search to include grey literature, and specialist resources such as clinical trials registers. Searching one database at a time enhances your search by making full use of the available subject indexing and search functionality.
Systematic reviews should encompass a wide range of information sources.
Searching databases
Guidance on subject databases – including how to access them, and how to plan, run, revise and save your searches – can be found on the Searching subject databases page, part of the University's suite of Studying effectively resources.
The online resource Searching systematically to find evidence for a systematic review includes demonstrations of how to run searches in various databases.
Subject databases
Search collections of articles by subject. Suggested databases for different subject areas can be found in our faculty-specific subject guides. Researchers at UoN can access these databases through our discovery tool, NUsearch, which also categorises databases by subject area.
Note that some databases use subject headings which enable you to search using controlled vocabulary terms, e.g. MeSH (used in MEDLINE, PubMed, Cochrane), Emtree (used in Embase).
Citation searching
Track individual research articles forwards and backwards in time. The following databases are excellent for this purpose:
Learn more about citation searching.
Resources for database searching
University of Nottingham Libraries has created video walkthroughs of key databases according to subject area:
For an introduction to systematic searching in PubMed, there is a one-hour online PubMed course produced by the University's School of Medicine.
AI tools in Evidence Synthesis
A variety of AI tools can be used during the systematic review or evidence synthesis process. These may be used to assist with developing a search strategy; locating relevant articles or resources; or during the data screening, data extraction or synthesis stage. They can also be used to draft plain language summaries.
The general view is that AI tools can be very useful in different stages of the systematic or other evidence review but that it is important to fully understand any bias and weakness they may bring to the process.
The guidance is that AI tools should be used in conjunction with existing validated methods. It is also essential to consider ethical, copyright and intellectual property issues for example if the process involves you uploading data or full text of articles to an AI tool.
NICE have issued this guidance: Use of AI in evidence generation: NICE position statement
Cochrane, JBI, Campbell have issued this joint draft guidance for consultation and revision: Responsible AI in Evidence Synthesis (RAISE): guidance and recommendations
For more information on AI tools see the King’s College LibGuide to Systematic Reviews
Grey literature and other sources
Grey literature is research which appears in a non-commercial or unpublished form and which may be targeted at consumers rather than an academic audience. It can be particularly useful in emerging areas of research where peer-reviewed publications are limited. Below are some sources you can consider:
Grey literature is not usually indexed like peer-reviewed articles and may not be as organised in its presentation or structure. Accordingly, your grey literature search could become time-consuming unless you set some parameters in advance. It may help to pre-decide which resources you will search and how much time you will devote to the search. For example, if searching Google, you could state that you will screen the first 200 results only.
Tip: When searching Google, use your browser's incognito mode in order to prevent the results being influenced by your previous search history.
More information on grey literature is available in the King's College London LibGuide on systematic reviews.
Dealing with your search results
Read our guidance on how to manage the references you identify whilst searching.
Saving searches and alerts
Many databases enable you to save searches and set up alerts.
- Saving searches means they can be re-run at the touch of a button, rather than retyping your terms from scratch.
- Alerts provide you with automatic updates when new, relevant articles are added to a database.