A problem with just keyword searching:
Running a keyword search returns documents that include or mention the term you searched for.
For example imagine you ran this search on diabetes mellitus type 2 in adults
The search results would include either:
Essentially a keyword search searches for words, not topics, which increases your chances of missing an important article that is about your topic.
One key strategy in making sure you find more precise and relevant articles based on your topic is understanding that most terminology with have alternate spellings and synonyms. Your search will expand if you can find ways to use alternate words to describe your topic. Additional terms we can use based on our topic above can be:
Keyword searching can be restrictive on how many results you get when you are conducting a literature search. Therefore many scholars who need to do a thorough literature search on a topic use controlled vocabulary. Controlled vocabularies group synonymous words under one main term: a Subject Heading. Conducting a search using Subject headings means researches find articles that are about their topic, rather than just mentioning the topic.
Examples of keywords and subject headings in PubMed and CINAHL