Tip #28: Exploding MeSH - PubMed vs. Ovid MEDLINE

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 A few years ago I ran into a search quirk when translating a lengthy search from PubMed to Ovid MEDLINE. My Ovid results were significantly larger and it wasn't immediately obvious what was happening. After much testing and consulting with my colleagues (thanks, Mark MacEachern!), we finally pinned it down to a single MeSH term returning vastly different results between the two platforms. 


Ovid - exp Food/ 1,428,580 results

PubMed - "Food"[Mesh] 701,490 results

We figured out what was causing the difference, but there was nothing in the help documentation that explained why it was happening. Even though the searches appeared to be the same, both MeSH terms were exploded, the platforms appeared to be handling them differently. I had to reach out to Ovid to get an answer for my remaining question. Over the course of a few weeks and many emails, they were finally able to provide a clear explanation: Ovid was including “Drug Terms” in the explode, where PubMed was not doing this. Ovid included corresponding drug terms for: Food additives, Flavoring agents, Sweetening agents, Micronutrients, Trace elements and Vitamins.

Based on our interaction, the Ovid Database guide was updated to includes this explanation (https://ospguides.ovid.com/OSPguides/medline.htm#tools):

"Note about Pharmacological Actions and MeSH tree for Ovid MEDLINE:

Unlike PubMed, Ovid MEDLINE only has 1 hierarchical tree. Therefore the Pharmacological Actions are included in the Ovid MEDLINE tree display as "[Drug Terms (Non MeSH)]". Secondly the "explode function" on Ovid automatically includes Pharmacological Actions when applicable.

Example: exp air pollutants/

  • Includes all MeSH terms for Air Pollutants: Air Pollutants/, "Air Pollutants, Occupational"/, "Air Pollutants, Radioactive"/, "Greenhouse Gases"

  • Includes all Pharmacologic Actions MeSH terms: Gasoline/, Hydrogen Sulfide/, Particulate Matter/, Radon/, Sulfur Dioxide/, Vehicle Emissions

  • Does not include the Supplementary Concept terms for Air Pollutants: 1,6-hexamethylene diisocyanate, 2-nitrofluoranthene, 2-nitrofluorene, bisphenol A, methyl tert-butyl ether, silicon nitride."

Moral of the story: Make sure to confirm how a platform or database executes hierarchical explosions when translating a search!

 

 

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