Boolean operators are the core of a successful and targeted literature search. Boolean operators are three simple operators you can use to connect your search terms and instruct the database on how to look for literature in a way that fits your research question.
There are three more important search techniques vital to developing a good search string. These techniques are used to structure your search and get exactly the results you need.
((healthcare OR "health care") AND ethics) NOT nurses
Subject headings, also known as thesauri, controlled vocabularies, or taxonomies, are a set of specific and controlled terms applied to research articles to clearly mark what topics a research article addresses. Subject headings:
As an example, let's look at MeSH, the subject heading system used by PubMed. The MeSH term Drug Therapy is used for any articles that reference drug therapy, drug therapies, chemotherapy, chemotherapies, pharmacotherapy, and pharmacotherapies. So when you are using PubMed, you can do a search for the subject heading Drug Therapy to get comprehensive results, even if the author was using the alternative terminology listed above.
Subject headings are a great way to get a comprehensive search without thinking of every possible synonym or language variation on your own, which also makes them ideal for quick searches on specific topics.
To use subject headings:
Note that every database uses its own subject headings system. When using a new database, try looking for terms such as Subject Headings, Index Terms, or Thesaurus in its navigation or help menus to find their subject headings. Database help or support pages may also provide guidance on using subject headings.
Turning a research question into a search string is a multi-stepped process:
As you do test searches and read more relevant literature, you will be able to add additional keywords to your search concepts. It is recommended that you reach out to a librarian for assistance in generating keywords and mapping concepts to a controlled vocabulary.
|Academic Search Complete
(MH "Obesity, Morbid")
DE "MORBID obesity"
|heart disease||heart disease
|"Heart Diseases"[Mesh]||(MH "Heart Diseases")||DE "HEART diseases"|
|"Stroke"[Mesh]||(MH "Stroke")||DE "STROKE"|
Once all terms have been identified, you need to put them together in a search string. You can export your search strategy in addition to the results, to use in your search documentation.
A search string will generally look like:
(Topic A term 1 OR Topic A term 2) AND (Topic B term 1 OR Topic B term 2) AND (Topic C term 1 OR Topic C term 2)
If searching PubMed with our example research question, the search string would look like:
(obesity OR overweight OR obese OR "morbidly obese" OR "Obesity"[Mesh] OR "Obesity, Morbid"[Mesh]) AND ("heart disease" OR "cardiac diseases" OR "heart disorders" OR cardiovascular OR "Heart Diseases"[Mesh]) AND (stroke OR "cerebrovascular accidents" OR "Stroke"[Mesh])
The search string above was developed for PubMed. When adapting the string for another database, you want to have the strings operate as similarly as possible. You would replace the MeSH terms with the controlled vocabulary of the other databases used.
The search string above is searching with both keywords and MeSH terms. The MeSH terms will be searched in the MeSH field. The keywords will be searched in all fields, like the title, abstract, journal name, etc.
In a systematic review, you will need to keep the search as similar as possible between different databases. In practice, you should only need to change a few things for each database:
As experts in database searching, librarians can help you translate your search string between different databases.