Language varies across time and place, so how you might describe a topic may be very different to how others may describe it. In some cases simply the spelling may be different. For these reasons using natural language, or keywords, in your search may not be successful.
Example: cancers may be cancer, carcinoma, neoplasms, tumours, malignancies and more
tumour itself may be tumour, tumours, tumor or tumors
In a natural language, or keyword search, you have no way of knowing if these variants are going to be found. One of the ways databases deal with this problem is to use a controlled vocabulary (also called subject headings). This means a consistent term from the controlled vocabulary (or subject heading) has been tagged (or indexed) to any paper dealing with that topic, no matter how it is described within that paper. The most common vocabulary is MeSH (Medical Subject Headings), used in Medline and PubMed.
Example: the MeSH term Neoplasms is used for cancer, cancers, neoplasia, neoplasm, tumor, malignancies, benign neoplasms and malignant neoplasms
Using the right MeSH term will identify a lot more literature around a topic than any single term will.
There are a number of ways to identify useful MeSH terms.
We have used MeSH as a shorthand for subject headings, as it is the most widely known. However other databases use different terms. Embase use Emtree and PsycInfo uses the American Psychological Association's Thesaurus of Psychological Index Terms. However these vocabularies work in the same way and the instructions for Medline will generally apply to these databases too.
For some topics there may not be a suitable subject heading, or the subject heading will not be specific enough. In other cases keywords alone will be able to identify relevant literature. For example:
Usually a combination subject terms and keywords is required to effectively target the most relevant literature.
For tips to manage issues of plurals and spelling or phrasing variations see the Search Tips tab.