Responsible Literature Searching Guide

Subject Headings/Controlled Vocabulary

As discussed in previous sections, databases are designed to make the search process more systematic. A key example is how databases handle search terms. Since it is possible to describe the same concept in different ways (i.e., cancer, neoplasm, carcinoma, tumor, tumour, etc.), select databases (i.e., PubMed, Ovid MEDLINE, Ovid Embase, CINAHL, APA PsycINFO, EBSCO databases) use a single authoritative term, known as a subject heading, controlled vocabulary, index term, or a thesaurus, for a given concept. The database producer "controls" the vocabulary by adding new and removing old terms.

The following table illustrates the different database's controlled vocabulary for the concept "breast cancer" and includes the database’s thesaurus, if available.

It is important to remember that not all databases have controlled vocabularies (i.e., Scopus and Web of Science). Understanding the differences between subject headings and keywords and the most effective ways to apply them will result in a more effective search.

Librarian indexers read, interpret, and assign the appropriate subject headings to describe the article’s content. Using the database’s subject headings or controlled vocabulary provides consistency, addresses spelling variations (American versus British), and can increase the precision or relevance of the search. It is important to remember that subject headings change across databases.

More Information

• See Appendix 1 - Controlled Vocabulary Tips for additional background and tips on how to use controlled vocabulary terms.
• Refer to the specific database's Help for more detailed explanations.

(CINAHL Complete, 2020; Jankowski, 2008; Patrick & Munro, 2004; U.S. National Library of Medicine, 2019; Walker & Janes, 1999; Wessel, 2019; Wolters Kluwer, 2019)

Keywords/Natural Language

If there is no match from the database’s automatic mapping, then proceed to keyword or natural language searching. Keywords are everyday language and can be used to search in the article’s title, abstract, specific search fields, or text field. Consider the author’s supplied keywords, synonyms, related terms, abbreviations, acronyms, generic drug versus proprietary drug names, etc. Using the author’s supplied keywords or natural language may be the best way to find relevant information when a topic is new. However, be aware that keyword or natural language searching may not retrieve all relevant citations because of either a mismatch with the author’s supplied keywords or an incomplete assignment of keyword or natural language search terms.

For example, keywords for the concept "breast cancer" can include but not be limited to:

More Information

See Appendix 2 - Keyword/Natural Language Tips for additional information on how to use keywords.

(Jankowski, 2008; Patrick & Munro, 2004; Walker & Janes, 1999; Wessel, 2019)

Subject Heading vs. Keyword Searching

The following table compares and contrasts searching by either Subject Heading or Keyword.

To be comprehensive, search using both subject heading (controlled vocabulary) and keywords (natural language):

• Not all databases have controlled vocabularies. Examples include Scopus and Web of Science.
• Controlled vocabulary limits retrieval to the time period in which terms are in existence or to articles that already have assigned terms.
• Not all indexing is done consistently.
• Articles that have not yet been indexed or are out of scope in MEDLINE (the largest component of PubMed) will only be retrieved using keywords or natural language. Examples include MEDLINE In-Process, Non-Indexed or Epub Ahead of Print articles.
• Articles that do not have an abstract or author-supplied keywords will be retrieved using controlled vocabulary or an exhaustive keyword search.

(Jankowski, 2008; Patrick & Munro, 2004; Walker & Janes, 1999; Welch Medical Library, 2019; Wessel, 2019)

Phrases, Truncation, Wild Cards

The following search techniques may be applied with keyword or natural language searching. Due to periodic vendor updates, it is recommended to check the database’s Help section to ensure you are using the correct search technique.

Phrases

Some databases require phrases to be put in double quotation marks, while others do not. Check the database’s Help section to confirm. For example, to allow its Automatic Term Mapping (ATM) process to find phrases, PubMed recommends to NOT use double quotation marks until you first try to search without them. If PubMed’s ATM does not map the concept to a MeSH term, adding the double quotation marks will force a phrase search.

Truncation and Wildcards

Truncation and wildcards allow the searcher to find word variations caused by plurals, adjectives, and alternate spellings (American versus British spelling).

• Truncation returns multiple spelling variations of a word root from the point of the truncation symbol.
• Wildcards allow you to substitute a symbol for a letter(s) within a search term or between search terms.

Some databases use the terms "truncation" and "wildcard" interchangeably. In most databases, the truncation symbol is the asterisk (*). Wildcard symbols include question mark (?), dollar sign ($) or hash mark (#). Check the database’s Help section to confirm if truncation and wildcards are allowed and, if yes, confirm the correct symbol. Also, review the database’s Help section on whether the database’s search algorithm ignores stop words (i.e., “a,” “about,” “and,” “not,” “of,” “or,” “the”) in the search query.

Examples:

• End of the root word – use the asterisk (*) at the end of the root to find spelling variations from the point of the asterisk (cancer* will return cancer, cancers, cancerous, etc.)
• Beginning of a word – use the asterisk (*) at the beginning of the root to find spelling variations from the point of the asterisk (*glycemia will return hyperglycemia, hypoglycemia)
• Within the word (s*food will return seafood, soyfood)
• Irregular plurals (wom?n will return woman, women)
• American and British spelling variations (gyn?ecology will return gynecology, gynaecology)

Note: Placing the truncation symbol too soon can retrieve unexpected results. For example, if you truncate diet* to get diets and dietary, you will also retrieve citations related to diethyl….

More Information

See Appendix 3 - Database Comparison Chart to view a chart that summarizes search tips by commonly searched databases.  This tool is helpful when translating a search from one database to another database.

(Elsevier, 2019; Jankowski, 2008; Patrick & Munro, 2004; U.S. National Library of Medicine, 2019; Welch Medical Library, 2019; Wolters Kluwer, 2019)

References

EBSCO. (2020). CINAHL Complete. Retrieved from http://support.ebsco.com/help/index.php?help_id=DB:937

Elsevier. (2019). Scopus: Access and use Support Center - Training;. Retrieved from https://service.elsevier.com/app/answers/detail/a_id/11213/supporthub/scopus/

Jankowski, T. A. (2008). The Medical Library Association Essential Guide to Becoming an Expert Searcher: Proven Techniques, Strategies, and Tips for Finding Health Information. New York: Neal-Schuman Publishers.

Patrick, L. J., & Munro, S. (2004). The literature review: demystifying the literature search. Diabetes Educ, 30(1), 30-34, 36-38. doi:10.1177/014572170403000106

U.S. National Library of Medicine. (2019, November 15, 2019). PubMed User Guide. Retrieved from https://pubmed.ncbi.nlm.nih.gov/help/

Walker, G., & Janes, J. (1999). Online Retrieval. A Dialogue of Theory and Practice (Second ed.). Englewood, Colorado: Libraries Unlimited.

Welch Medical Library, J. H. U., School of Medicine. (2019). Expert Searching. Retrieved from https://browse.welch.jhmi.edu/searching

Wessel, C. B. (2019). Responsible Literature Searching for Research: A Self-Paced Interactive Program. Retrieved from https://cme.hs.pitt.edu/ISER/app/learner/loadModule?moduleId=8381&dev=false

Wolters Kluwer. (2019). Ovid Help. Retrieved from http://site.ovid.com/site/help/documentation/osp/en/index.htm#CSHID=advanced.html