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Medline Guided Exercise: 2. Subject Heading Search

2.  Subject Heading Search

In this module you will learn how to find relevant subject headings for our first, or P, element.

Remember, for each PICO element we will perform both a Subject Heading and a Keyword search. Each type of search has different advantages that will make our search more relevant.

Let's begin with the Subject Heading.

What is a Subject Heading?

  • Subject headings describe the topic of a paper, similar to tags or hashtags
  • They are pre-defined, controlled vocabulary that standardizes and pulls together synonyms, spelling and different word endings
  •  In Medline these are known as MeSH (Medical Subject Heading)
  • These tags are added to the record in the MeSH, or descriptor field, by indexers who have read the paper
  • In a subject heading search, the search engine looks for and finds a match in the MeSH or descriptor field

Tip: Beginning a search design with a subject heading is good practice as the information in the Scope Note and Tree will help create the subsequent keyword search

For this guide we will consider the research question: "What research has been done on the use of games such as Wii, Kinect and others for improving balance in children and teenagers who have a traumatic brain injury including concussion."

Start building your search using the first PICO element, the concept for Problem/Population.  For this part of the exercise we will use the search term: brain injury

Step by Step: Subject Heading Search

Identify the Subject Heading

  1. In the Medline Ovid search box
    • Enter the first PICO concept: brain injury
    • Ensure that the checkbox “Map Term to Subject Heading” is selected
      • This will find potential MeSH related to your search term. We will use the Scope note and Subject Tree to decide which is most relevant.
  2. Click Search.
  3. You will now see the Mapping Display
    • It shows one or more possible subject headings (in blue) related to our search term. The last term in the list, which is displayed in black, is a Keyword which we will cover in the next Step.
    • In this case: Brain Injuries is the only option
  4. To Decide If this is the most relevant MeSH for our topic, check the Scope note and Tree
Video demo: Identify the Subject Heading

Checking the Scope Note

Before deciding on which subject heading is the most relevant, we need to read the Scope Note

  1. Let's examine the MeSH: Brain Injuries
  2. Click on the to open the scope note
    • From the definition, Brain injuries seems appropriate
    • The time period is adequate
    • Under "Used For", there are different forms and synonyms that are covered by this MeSH. These are useful for our Keyword Search
  3. Return to the mapped list by clicking on Previous Page
Checking the Scope Note
Video demo: View the Scope Note

Checking the Tree

The Subject Tree
  1. Click on the link for Brain Injuries to open the Tree
    • Brain injuries is highlighted in blue
    • There are more specific terms indented beneath it, including Brain Injuries, Traumatic
  2. Click on the + icon to expand Brain Injuries, Traumatic
    • There is a more specific search term indented beneath: Brain Concussion
  3. Select the check boxes for both Brain Concussion and Brain Injuries, Traumatic
    • As these are most relevant to our topic
  4. Deselect Brain Injuries
    • As this is too broad
  5. Click Continue

Note: Our search with the number of results is displayed in the Search History as Set 1. The words in the search history have a forward slash / (e.g. brain injuries, traumatic/). This symbol indicates that they were used as a subject heading.

Video demo: Subject Tree

Explode and Focus Tools


The Explode tool selects the selected heading as well as any narrower terms that are indented below it. This is a useful shortcut, for example, Explode Canada will find papers that are tagged with the heading of Canada as well as any that are tagged with the Provinces. As in some trees the indented terms are not relevant to the research question, an alternative to Explode is to be selective and choose ones that are relevant.

In our example, selecting Explode for Brain injuries will include all the narrower terms indented below it in the list. Many are irrelevant to our topic and so we chose to select only the most appropriate.


The Focus tool will only search for those articles where the topic is the main point of the paper. Where a subject heading has been designated as the main point (or focus) of the paper, it is identifiable by an * in the search history and MeSH field.

  • Focus can be useful when needing a few very relevant papers on a single topic
  • It is usually not used when doing a comprehensive search for a Systematic Review, nor when there will be other search elements in the strategy.

As we will be constraining our search with other terms from the PICO, we will keep the search broad and not use Focus for Brain injuries

Video demo: Explode and Focus

Find the Subject Heading for your P Concept

Following the steps outlined above, find the most appropriate subject heading (MeSH) for your first concept.

  • From the list of potential subject headings1, decide what MeSH you will use for your search by checking the Scope note:
    • Does the definition, or scope, match my concept?
    • Is there a year of entry and does it cover the time period I need?
    • Are there any other MeSH terms to consider for my topic?
    • Does the list under Used For cover my topic?
    • Do these words suggest synonyms I can use in my keyword search?
  • Use Previous Page to return to the list of potential subject headings to check the Tree
  • When checking the Tree you will be looking for the most specific MeSH for your topic
    • Are there other broader or narrower MeSH terms that match your P concept?
  • Select any MeSH that apply to your P concept. [Note: if all are relevant use the Explode tool]
1 The term displayed in black is the Keyword form ( this will be addressed in the next Step.

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  • Tip: Use your PICO sheet to track your decisions and to note any clues to additional search terms.