What is a subject heading?

This video explains what a subject heading is, how and why to use them when researching, and explains what an exploded search is.

Transcript:
Searching with subject headings is a powerful alternative to searching with keywords, but it helps to understand what a subject heading is, and how it works, so you can use them effectively when searching a database.

This video will show you: what a subject heading is, and how they are different to standard keywords; how subject headings are organised in a hierarchy, and how that helps you search; and when subject headings are most useful.

If you need to know how to use subject headings in a particular database, check our other materials and resources, or contact the library for help.

You have probably already seen subject headings, when searching in databases. Sometimes they are called subject terms, index terms, or index keywords.

A subject heading is a short topic description, taken from a defined list of terms, which is organised into categories. These categories are then arranged in order from very broad, to very specific.

Subject headings do two things that keywords don't: they give us a single, consistent description of a topic, and they are organised into categories.

A very common issue when searching, is figuring out all the ways a particular topic might be described.

If I was looking for information about patient peer support groups, I would need to think of all the ways that concept could be discussed in the research literature, and come up with a list of keywords and phrases.

Then I would put those synonyms together in a search, to find the relevant papers.

To make searching easier, one single subject heading is created, and that label is applied to every source that discusses that topic. Once you know which subject headings apply to your topic, you can search with that one label.

The organised category, or hierarchy structure of subject headings, can also help you search more effectively.

Let's say you're looking for information about eye infections. This set of subject headings is organised in nested categories: at the top is the subject heading for Eye Diseases, then underneath we have headings for different types of eye diseases, like Eye Injuries and Eye infections.

Then underneath Eye Infections, there are even more specific headings for different types of eye infections.

If I do my search with the heading 'Eye Infections' and get too many results, I could try using 'Bacterial Eye Infections' instead, for a smaller, more specific set of results.

On the other hand, if I used 'Eye Infections' combined with a keyword search, and didn't get enough results, I could try using 'Eye Diseases' or a combination of subject headings to get more results.

The structure of subject headings also lets us do what is called an 'exploded search'.

An exploded subject heading search, will search for your selected heading, AND all the subject headings underneath it, and all the headings under those.

Let's say you're still looking for information about eye infections. This article is about trachoma, a type of bacterial eye infection. This article is about herpes zoster ophthalmicus, a viral eye infection. There is a specific subject heading for both of these conditions. This article is about a variety of different fungal eye infections, so *it* just has the general subject heading 'Fungal eye infections'.

If we do an exploded search for the subject heading 'Eye infections', we would get all three of these articles in our results, because our exploded search looks for all the subject headings under that the heading 'Eye Infections', as well as the heading itself.

Now you know what a subject heading is, and how one works, when should you use them in a search?

Subject headings are most useful when: you have lots of synonyms, as we saw with the our peer-support group example; when a topic is hard to describe in a short phrase; when you want to search across a whole category of topics; or when you are performing a systematic search, and need a more rigorous searching method.

In this video, you learned: what a subject heading is, how they are organised in a hierarchy, how an exploded search that uses the hierarchy structure can expand your search, and when subject headings are most useful.