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The EBM Medical Literature Search: Nesting

FAU Medical Library

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Nesting  is a way to bring back highly relevant results based on your research question. This is a strategy to take your simple Boolean Operator search (AND, OR, NOT) and make it more focused. When nesting, you are using a combination of Boolean Operators with symbols such as parenthesis, quotation marks, and truncations. Databases will read the information in the parenthesis first: using them organizes how your search string is read and will change the results you retrieve.  Boxes on this page how examples of how this works in a search. 


Embase Example

Without nesting:


children AND "duct tape" AND warts AND cryotherapy

16 results

In this example, we are using our PICO keywords established earlier in this guide. Entering the terms straight into the search fields we get 16 articles back. 

Here is a visual breakdown of the search: 

  • children+"duct tape" + warts+ cryotherapy


With Nesting:

(children AND warts) AND  ("duct tape"  OR cyrotherapy) 

20 results

However, we are going to adjust our search string to see if we can get additional articles that pertain to our subject. We are now also looking for articles that contain children +warts, and either "duct tape" or cyrotherapy. The articles may still contain both terms but we want to mainly see if we can get any additional articles with either single term back without running separate searches. 

Here is a visual breakdown of the searches occurring simultaneously:

  • Children+ warts+ "duct tape"
  • Children + warts + cyrotherapy
  • children+ warts+ "duct tape"+ cryotherapy

Pubmed Example

Without nesting: 

"Avian flu" AND transmission OR infection

1.6 million results

In this example, the parenthesis was omitted. We are seeking out articles with the full term "avian flu," however the order of operations views the AND as a single unit, and the OR as an add on.  

Here is a visual breakdown of the search:

  • "Avian flu"+ transmissions
  • Infections

With nesting:

"Avian flu" AND (transmission OR infection)

210 results

In this example, we are looking for articles that contain the full term "avian flu." We want articles containing the full term to also include either the word transmission or infection. The articles may contain both the terms, but will have at least one of them in reference to "avian flu". 

Here is a visual breakdown of the searches occurring simultaneously:

  • "Avian flu"+ transmission 
  • "Avian flu"+ infection
  • "Avian flu"+ transmission+ infection 

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