Studies for your syntheses may be found in the form of:
Deciding where to search will largely depend on the review type and topic. How many resources you search may depend on time constraints. Locating studies for syntheses often includes searching for both published and unpublished ("grey") literature.
Queen's University Library provides access to broad coverage databases in medicine and the health sciences (such as MEDLINE and Embase) as well as smaller subject-specific databases (such as PsycINFO and CINAHL). Depending on your review topic, it may also be appropriate to search in databases from other disciplines such as the social sciences, law or education.
Below is a list of the most popular health sciences databases used for syntheses that Queen's University Library provides access to. It is not a comprehensive list of potentially relevant databases. To discover more databases that might be relevant for your topic, try the Browse Databases by Subject feature on the library website or speak with a librarian.
PubMed versus Ovid MEDLINE: Did you know?
You can search MEDLINE using PubMed or the Ovid interface. PubMed is a free resource that you will always be able to access, whereas Ovid MEDLINE is a proprietary resource that has been purchased by Queen's University Library. The Ovid interface allows adjacency searching, which PubMed does not, and may be more user-friendly for new searchers than PubMed.
What is grey literature?
Grey literature is the term used to describe literature that is not formally published as a book or journal article (Higgins, 2011), including:
Related library guides:
Grey literature resources:
Some library databases contain grey literature in addition to journal articles. For example, PsycINFO includes dissertations; Embase and Medline/PubMed include conference proceedings. Library databases like Medline/Pubmed, however, do not provide comprehensive coverage of grey literature so other resources should be searched to identify literature that is not formally published.
Clinical trials registries:
For quantitative systematic reviews of healthcare interventions, it is strongly recommended to search clinical trial registries for on-going and unpublished trials in order to limit publication bias. Refer to Section 6.2.3 Unpublished and Ongoing Studies in the Cochrane Handbook for Systematic Reviews of Interventions for more information.
Hand-searching relevant journals page by page can be incredibly time-consuming but it may identify additional studies that have been missed by database search strategies or studies from journals that are not covered in electronic databases.
Hand-searching conference proceedings:
Databases may not index conference proceedings, and even if they do, coverage may be limited. Hand-searching relevant conference proceedings that are available on association or conference websites may identify additional relevant studies.
Once you have identified eligible studies for your knowledge synthesis by searching the appropriate resources above, it is best practice to then check the reference lists of these studies to identify any additional studies. The reference lists of related reviews may also help to identify additional studies.
Citation indexes such as Web of Science (or the search engine Google Scholar) can be used for cited reference searching. Citation reference searching allows you to identify where eligible studies have later been cited to see if this identifies any additional studies. For example:
If you search for a relevant study in Google Scholar you will see a "Cited by..." link underneath the study information that indicates how many times the study has been cited (unless the study has not yet been cited). You can follow this link to view where the study has been cited to see if this locates any additional studies.
For more information, refer to the section on Citation indexes in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins, 2011).