In-Depth Database Tutorial: PubMed

Keywords — How to find synonyms and be comprehensive

• To begin the keyword portion of any search, always repeat the MeSH term as a keyword without the MeSH command [Mesh]. In this case, "Atorvastatin" should be the first keyword, and this tutorial will show you how to add this keyword to the search with MeSH terms in the next section.

• In the meantime, the next step is to find synonyms for this keyword. Fortunately, synonyms can be conveniently located within any MeSH record within the section towards the middle of the page labeled "Entry Terms." As seen in the following screen-capture, the entry terms for the drug Atorvastatin are synonyms, alternate forms, and other closely related terms generally used interchangeably:

• Note that keyword terms can be single words or phrases. Use quotes around all phrases to ensure that the phrase is searched instead of each word individually (e.g. “public health”). In the case of Atorvastatin, consider the synonym of Atorvastatin Calcium Trihydrate. If searched for without quotes, the search algorithm will retrieve results about "Calcium," "Atorvastatin," or "Trihydrate." To ensure that results are only retrieved with all three terms side-by-side as a single phrase, quotes around all three together are necessary ("Atorvastatin Calcium Trihydrate"). The difference between searching separately and with quotes is 9,449 results (for no quotes) vs. 6 results (w/ quotes). 

• ​Pro tip: consult controlled vocabularies in other subject databases for additional help. For example, the Embase has a controlled vocabulary called Emtree. Emtree records contain synonym lists similar to the "entry terms" in a MeSH record.  The Emtree synonym list often contains European spellings/variations.

• In the case of Atorvastatin, it is advisable to use all the entry terms pictured above as synonyms. Again, in the next section labeled "Sample Search Step 3: Combining Searches Using Boolean Operators," screen-captures and instructions will be provided to explain how to search for all these synonyms at once, combined with the MeSH term for Atorvastatin. First it is worth considering the following two asides on the important concepts of field tags and Boolean operators (AND, OR, NOT).

Aside: Applying field tags to keywords

You can use field tags to specify where the database looks for the keyword search term. This can be important for keyword terms that are general and might be included in the titles of institutes, universities, and/or journals. For example, searching the keyword "ethics" without a field tag will bring up results from the Journal of Clinical Ethics and/or results by authors affiliated with the Institute of Biomedical Ethics and History of Medicine at the University of Zurich. To ensure that results are focused on searching the title and abstract of an article, it is highly advisable to use the third field tag listed below [TIAB]. There is an extensive listing of field tags provided by PubMed (full listing of different field tags),

To utilize the following recommended field tags, first type the search term and then the field tag in brackets. e.g. Atorvastatin [tiab] looks for cardiology in the title and abstract.

• [Title/Abstract] or [tiab] – Words and numbers included in the title, collection title, abstract, and other abstract of a citation. English language abstracts are taken directly from the published article. If an article does not have a published abstract, NLM does not create one.

• [All Fields] or [ALL] – Untagged terms and terms tagged with [all fields] are processed using Automatic Term Mapping. Terms enclosed in double quotes or truncated will be searched in all fields and not processed using automatic term mapping.

• [Text Words] or [TW] – Includes all words and numbers in the title, abstract, other abstract, MeSH terms, MeSH Subheadings, Publication Types, Substance Names, Personal Name as Subject, Corporate Author, Secondary Source, Comment/Correction Notes, and Other Terms.

• NCBI explanation of Field Descriptions and Tags 

Aside: Applying Boolean operators to keywords

• Boolean operators are used to combine search terms. In PubMed, you can use the operators AND, OR, and NOT.

• ​Boolean operators MUST be used as upper case (AND, OR, NOT).

  • OR--use OR between similar keywords, like synonyms, acronyms, and variations in spelling within the same idea or concept

• AND—use AND to link ideas and concepts where you want to see both ideas or concepts in your search results

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• NOT—used to exclude specific keywords from the search, however, you will want to use NOT with caution because you may end up missing something important.

• In the case of combining synonyms for Atorvastatin, it makes sense to use the OR operator because we want to retrieve results that include as many articles as possible on the drug (i.e. we want results discussing Atorvastatin OR [synonym #1] OR [synonym #2])

• Go to the next section to see how all of these keyword synonyms can be combined into a single search phrase using OR and the field tag [tiab]