Ovid databases

• Type your first concept - e.g. epilepsy - into the search box and make sure that the Map Term to Subject Heading box, below the search box, is ticked. In most databases this will be ticked by default. This means that when you click Search, you will be searching the thesaurus for your search term.
• Click Search and the thesaurus feature will try to identify subject headings related to your concept and display them as a list.

• Click on a subject heading to view more information about it and to find out how it relates to other subject headings. Some databases display subject headings in a ‘tree’ structure, showing broader and narrower terms. Others display them alphabetically.
• Explode: tick this box to search for the selected subject heading plus any narrower terms. E.g. If you explode the term 'Epilepsy' in Medline, you also find records with the related subject headings Epilepsies, Reflex; Epilepsies, Partial, etc.
• Focus: tick this box to limit your results to only those records where your chosen subject heading is the main topic. This can be useful for finding a few key papers on a subject, but is not recommended if you want to do a comprehensive search.
• Scope: click the information icon in the right column to see a definition and other additional information, including any older terms used to describe your topic. Always check the scope note carefully to make sure the subject heading you have found is the correct one. Sometimes you might not find the right one the first time so think of another way to describe your concept if you get an unexpected result, e.g. the subject heading 'mole' in Medline refers to small furry animals; you may need the subject heading 'nevus' for the skin malformation. 
• Select one or more subject headings from the list and combine them using AND or OR from the drop-down menu at the top.

Tip: the final entry in the list offers the chance to do a simple textword search, instead of, or in combination with, the subject headings. As this entry is not a subject heading, it has no Explode, Focus or Scope options.

On the following screen you may have the option to select subheadings.

Each database has its own thesaurus, so the subject headings which you find might differ when you search a different database.

In some databases, subject headings are called descriptors or index terms. In Medline, subject headings are called MeSH (Medical Subject Headings).