Library Services have produced subject guides to help you to find out more about the resources relevant to your subject area and about the tools on offer to help you with your research. Find the guide for your subject area and explore the Databases tab to learn more about key databases for your subject area.
What databases should I search/how many databases should I search?
The Cochrane Library Handbook suggests Medline, Embase, and CENTRAL as a minimum (if you are undertaking a medical intervention-based systematic review).
As a general guide you should also choose the databases most relevant to the subject area of your systematic review e.g. PEDRO for physiotherapists, CINAHL for nursing/allied health or PsycInfo for psychiatry/psychology type questions. Web of Science or Scopus are also good broad-ranging databases worth investigating to see whether relevant results are retrieved.
How do you know what you are missing/when can I stop searching?
In your search strategy you are aiming to reach a compromise between precision/specificity (the results are on your topic and relevant for you) and sensitivity (where you are as inclusive as possible in order not to miss any useful results). Systematic reviewers often err more towards being as inclusive as possible but this can generate huge numbers of results (particularly if you are searching across multiple databases). To be practical therefore most systematic reviewers will create search strategies that are precise enough for them to able to cope with the number of results that are returned, but use different methods of searching, e.g. both subject headings and keyword searching (in the databases that allow this) and searching multiple databases (where articles may be indexed differently or a very similar search retrieves results in a different way) to ensure that relevant results are not missed.
The Campbell Collaboration's Searching for studies: A guide to information retrieval for Campbell Systematic Reviews discusses the range of databases to be used and says:
"Given the multidisciplinary nature of most social science research questions and the large selection of social science-related databases, searches must be implemented in multiple databases. Terminology (both keywords and controlled vocabulary) will vary across these databases as different disciplines often use different words to mean the same thing."
They provide a comprehensive list of the databases in the social, behavioural, education and health sciences in the Appendix but suggest that the more frequently used subject databases include:
You can access these via the Databases A-Z List.
Library Services provides access to an extensive range of electronic resources to support teaching, learning and research across the Health Faculties. Look at the databases tab of your library subject guide to learn more about what databases might be relevant to your subject area and how to access them.
Some databases, e.g. Medline, will be searched by most systematic reviewers undertaking reviews in the health area, whilst others may be more subject specific, e.g. SciFinder for chemistry/pharmaceutical science or the Nutrition and Food Sciences CABI database for systematic reviews in that area.
Remember that you should always search one database at a time in order to make the most of the advanced features rather than cross-searching multiple databases even if that is offered as an option on a particular platform, e.g. search Embase and Medline as separate databases even though they are both on the OvidSP platform. This is essential for effective searching for systematic reviews.
If you are NHS staff you can use the Healthcare Databases Advanced Search with your NHS OpenAthens to search Medline, CINAHL, EMBASE, British Nursing Index, etc. See more information on searching the journal literature on the NHS Library Guide.
Remember that you should always search one database at a time in order to make the most of the advanced features rather than cross-searching multiple databases even if that is offered as an option on a particular platform, e.g. search Embase and Medline as separate databases even though they are both on the HDAS platform. This is essential for effective searching for systematic reviews
The debate as to whether Google Scholar should be used in systematic reviews, either as one of the databases searched, or potentially as the only database needed in a search of the medical literature continues. A study in 2013 (Gehanno et al) found that Google Scholar included all original studies which had been included in 29 Cochrane Systematic Reviews (738 original studies). The conclusion drawn by Gehanno et al was that the authors of these systematic reviews could have searched only Google Scholar rather than all the bibliographic databases they did and found the same results.
If you are interested in reading more about this then the following articles and discussion may be of interest.
These guides will guide you toward key databases for your subject and help you create effective search strategies.
The Medline database is one of the key databases to be searched by anyone undertaking a systematic review in the health, clinical and life sciences fields.
Medline can be searched on a number of different platforms including PubMed, OvidSP (accessible by Kings staff and students) and the NHS HDAS database platform (accessible by NHS staff) among others. Whilst it is possible to undertake searches for systematic reviews on the PubMed platform you may find it easier on one of the other platforms with Medline where it may be clearer for you to specify exactly what you are searching for and to combine your selected subject headings (MeSH terms) with free-text keyword terms.
When you search the Cochrane Library you are searching across a number of different databases, including Cochrane systematic reviews, systematic reviews published elsewhere and the Cochrane Central Register of Controlled Trials (CENTRAL).
"CENTRAL is a highly concentrated source of reports of randomised and quasi-randomised controlled trials. The majority of CENTRAL records are taken from bibliographic databases (mainly MEDLINE and Embase), but records are also derived from other published and unpublished sources. In addition to bibliographic details (author, source, year, etc.) CENTRAL records will often include an abstract (a summary of the article). They do not contain the full text of the article.
Each Cochrane Review Group maintains a collection of reports of controlled trials relevant to its own area of interest. These are called Specialised Registers. Unique content (i.e. records not already identified in MEDLINE, etc.) from these Specialised Registers is also published in CENTRAL. Groups may also collect items that are not relevant to its own field of interest; known as hand search results, which are added to CENTRAL as well."
Information taken from the About Cochrane Central Register of Controlled Trials (CENTRAL) webpage.
CENTRAL is therefore only going to be a database of interest to you if you are interested in retrieving randomised and quasi-randomised controlled trials (some areas of research may not be suitable for RCTS; whilst some systematic reviewers are specifically excluding RCTs as they are focusing on qualitative research). If you are not sure, it would be worth undertaking a basic search on CENTRAL to see what is retrieved.
Advanced searching using the Search Manager and MeSH Medline subject headings is also available on the Cochrane platform.