MEDLINE and CINAHL have yet another tool for narrowing your search results: Subheadings. These are not to be confused with SubJECT Headings, but they are closely associated with them.
Once you select a particular SubJECT Heading to use in your search strategy, the database will offer a list of subheadings that are specific to that term, which will help to focus on a particular aspect of the topic.
For example, suppose you are researching the West Nile Virus. Here is the list of subheadings offered by Ovid MEDLINE for that term:
What particular aspect of this virus are you interested in? If you are mostly interested in the genetics of this virus, then you might select the Genetics subheading. If you are interested in the immunology of the virus, then choose that subheading. If you are interested in many aspects, then you're better off accepting the default of All Subheadings.
The use of subheadings will almost always result in a smaller set of results, sometimes very much smaller. That can be helpful in some situations because the results will be very narrowly focused on that particular aspect of the topic.
However, just as with the Focus feature, when you use subheadings, you run the risk of missing relevant articles. That's because whether or not a particular subheading is assigned to the article is a highly subjective decision, especially since some subheadings can be quite similar, e.g., Genetics vs Immunology vs Physiology.
1. Subheadings may be useful when you are in the initial stages of a search on a very broad topic, because they will bring up articles that are known to be "on topic". After you have read those articles and gained familiarity with the topic, you can then revert to searching on "All Subheadings" to conduct a more thorough search.
2. Subheadings may be useful when the topic you are searching is very broad, e.g., diabetes, stroke, heart disease, and you need some tool to drop the numbers and help narrow the results.
3. Subheadings may be helpful in situations when you just need something good, quickly. This can be a huge time-saver.
Bottom Bottom Line: Use subheadings with caution, and remember that they may drastically reduce the number of results.