4. Combining Searches

Very often our searches are not confined to one topic.  We search for articles on one or more of the following:
  1. Measles in children
  2. Incidence of malaria and typhoid in India and Bangladesh
  3. Articles written by BD James in the New England Journal of Medicine
  4. Articles on lung cancer which do not cover chemotherapy with cisplatin
Every query has more than one term.  These can be combined using the terms AND, OR and NOT. These simple words have a slightly complex name - "Boolean Operators"

Boolean AND is used when we definitely want two or more of our search terms appearing in our search results
Boolean OR is used when we want any one or more of our search terms appearing in the results
  • Example: Diarrhea OR Malnutrition will get us articles that contain Malaria alone or Malnutrition alone or both terms coming together
Boolean NOT is used when we wish to eliminate one or more terms.

Important tip:

If you wish to do a very thorough literature search in some contexts (eg if you are writing an exhaustive literature review), then it is good to supplement a NOT search with an AND search. To explain clearly - if you do a search:
  • Pregnancy NOT lactation
You are eliminating articles that cover pregnancy but do not cover lactation at all. Great
But if there are articles that cover both terms, then when you type NOT lactation in the search box, you are eliminating such articles. So you lose information about pregnancy that may be valuable

So, it is good to then run a search - Pregnancy AND Lactation and hand pick articles that may have useful information about pregnancy