Combining terms with Boolean Operators (AND, OR, NOT) on Ovid databases

As covered in Module 2 Section 2, Boolean Operators are specific words used to combine search terms to improve the chances of finding relevant information. Concentrating on one part of your question at a time and entering search terms separately means that the structure of your search strategy is much easier to follow and it is much simpler if you decide later to delete or amend one component of your search.

The most commonly used Boolean Operators are AND, OR, and NOT.

  • Using AND looks for records that contain both terms. It decreases the number of results
  • Using OR finds records that contain either term. It increases the number of results
  • Using NOT will exclude all records that contain a term. It reduces the number of results

Use brackets when combining terms using Boolean Operators to ensure your search is processed in the way you intend. AND is processed before NOT or OR. OR is processed last. For example:

  • children OR adolescents AND obesity will find records about adolescents with obesity as well as all records about children. It will probably return a large number of records.
  • (children OR adolescents) AND obesity will find records about children with obesity or adolescents with obesity.

Watch Using Boolean Operators to learn how to combine search terms.
Playing time approximately 13 mins.

Activity 4: Combining concepts in your search

Practice your searching skills on the MEDLINE database. This activity enables you to practice combining concepts in a real search using Boolean operators.

You might like to print this instruction page to refer to as you complete the activity. Once you have printed the page, Open MEDLINE. For this activity we used the example of a patient with Type 2 diabetes, and the potential risk of cardiovascular disease. To this point we have searched for each concept separately. The next step is to use Boolean Operators to combine these searches.

  1. Notice: The ready-made search history you can see shows the results of all our searches and that each of these has found many thousands of articles. You can also see that each step of our search has been numbered
  2. Click the tick box next to search number 3 and 4 and then click the ‘OR’ button. This will return a combined result (a 5th search) of articles that contain either (or both) of the terms ‘Cardiovascular disease’ and ‘Diabetic nephropathies’ (search numbers 3 and 4). You can see that this has increased the number of results
  3. Click on the red ‘Expand’ button to the right of the search history to see all the searches
  4. Click the tick boxes next to searches 1, 2 and 5 and then click on the ‘AND’ button to combine them. This will return a combined result (a 6th search) of articles that contain all the terms in these searches: diabetes mellitus, type 2 and hypertensive agents and either cardiovascular diseases OR diabetic nephropathies. You can see that this has reduced the number of results
  5. Notice: We now have a search result that combines all three PICO concepts of our question: the problem or population (P), the intervention (I) and the outcome (O)
  6. Scroll down the page to have a look at the results. You will see that they are not all relevant to our specific question yet. In the next section we will look at applying some limits to the search to increase the relevance of the results
  7. Try doing a search on a topic of your interest. Use a minimum of 2 concepts. Search for each concept separately and then practise using the Boolean operators ‘OR’ and ‘AND’ to combine the concepts.