A critical element of a successful search is knowing how specific your search terms need to be. At the beginning, a few keywords may be enough to get started, but a sophisticated or systematic search requires more thought and depth. Subject headings are a great shortcut for general searching and are a hallmark of systematic searching.
What are subject headings?
Subject headings are a type of controlled vocabulary, meaning each term has a specific definition or context. They are applied to articles after a review of the content to group topics together, which is useful when ideas can be expressed many ways. Subject headings are relatively stable over time, whereas the language used by authors in a field can change quickly.
It's important to note that not all databases use subject headings. Different databases also use different vocabularies, so the terms applied will change between databases.
What are keywords?
Keywords usually reflect the language used by authors in the research literature, meaning the same idea can be expressed a lot of different ways. For example a search for "motorway" will find primarily European literature, whereas "highway" is more likely to find research from the US on the same topic.
Even when using subject headings, keywords are a useful addition to your search. There may not be a subject heading that perfectly captures your topic, so it is useful to include the language used by authors to narrow your topic. Some newer articles might not have been assigned a subject heading yet (or even assigned an incorrect heading!) and you would still want to include them in your results.
What should I use in my search?
A comprehensive or systematic search will use both subject headings (for precise language) and keywords to find all relevant results. Searching is an iterative process, so try different combinations of subject headings and keywords in conjunction with other search strategies (truncation, phrase searching etc) and filters to find the best results for your search query.
To find as many relevant studies as possible, you'll need to include as many relevant keywords as possible in your search. Let's examine an example research question.
Do e-cigarettes assist young people with smoking cessation?
If we search in a database (say, PubMed or FiNDit) using some of the words in this question (e.g. e-cigarettes, or smoking cessation), we can use words from the results to start to compile a list. You can also use an online dictionaries or encyclopaedias to search for synonyms. It's OK if your initial list of keywords isn't perfect to begin with or changes over time. Feel free to add or remove words from your list as you get more experience with searching.
Concepts and Keywords (Initial brainstorm)
| E-cigarettes | Young People | Smoking Cessation |
| Vapes | Teenagers | Giving up smoking |
| Electronic cigarettes | Young adults | Stop smoking |
| Digital Vapor Cigarette | Adolescents | Smoke free |
| Juul [brand name] | Undergraduates | Quit smoking |
Review the video below from Ohio University Libraries, which shows you how to gather and combine keywords for an effective search.
Subject headings are terms assigned to article records which describe an article's (or book's) content. Subject headings are usually assigned by the database itself (not the author), not the author of the work. As databases contain content from many countries, contexts, and disciplines, subject headings are a useful way to provide consistent language to describe contents.
As an example, let's look at the subject heading Ability in the database Psychology and Behavioral Sciences.
| Subject Heading | Used for the similar terms | Narrower Terms |
| Ability |
Aptitude Proficiency Skill Talent |
Academic ability Athletic ability Business skills Cognitive ability (plus many more) |
In databases such as Google Scholar that don't have subject headings, a person could search for the word "Ability" and only find articles that match the one word Ability. However, if someone searched for the word Ability in the Psychology and Behavioral Sciences database, they would also get articles that focus on concepts of Aptitude, Proficiency, Skill and Talent, which are very similar concepts to Ability. This means that you would get more relevant articles by using subject headings in addition to keywords.
Narrower terms are concepts that sit underneath the main subject heading in a hierarchy. In the table above, you can see that Athletic ability and Academic ability are sub-types of ability. To learn more about subject headings, view the video below or the Learn More section on this page.
Keywords can be used in multiple databases, while subject headings are unique to specific databases. This means that you will need to modify your search strategy to suit each database you use.
See Flinders University table to check your syntax.
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