Cochrane Library Tutorial
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MeSH Terms Explained

MeSH (Medical Subject Headings) is the (U.S.) National Library of Medicine's controlled vocabulary thesaurus and is used for indexing articles for MEDLINEGlossary link image. It is a set of terms naming descriptors in a hierarchical structure that enables you to search at various levels of specificity.

MeSH descriptors are arranged in both an alphabetic and a hierarchical structure. At the most general level of the hierarchical structure are very broad headings such as "Anatomy" or "Mental Disorders." More specific headings are found at more narrow levels of the eleven-level hierarchy, such as "Ankle" and "Conduct Disorder." There are 22,568 descriptors in MeSH.

Further explanation on MeSH and a quick tutorial can be found on the National Library of MedicineWebsite (U.S.A.). This should take less than 10 minutes to view.

The MeSH Database is available from the MeSH Search link in the menu at the top right.

Use the MeSHGlossary link image database to find MeSH terms including Subheadings, Publication Types and Pharmacological Actions. The MeSH database can be searched by MeSH term, MeSH Entry Term, Subheading, Publication Type, or words within a MeSH Scope Note. Subheadings and Publication Types are included in the MeSH term searches.

Subheadings are used with Medical Subject Headings (MeSH) to retrieve frequently discussed aspects of a topic, e.g., drug therapy, diagnosis, economics, psychology, etc.

How do I put these terms into my search?

Once you have found the MeSH terms that you want to search, you need to get them into the query box in a form that Cochrane can understand. One approach is to type each term in yourself, taking care to get the spelling and syntax correct. This can be difficult, particularly for a complex search. If there are lots of "AND" and "OR" terms in your search, then you have to group terms using brackets, which can also become confusing.

There are a couple of ways we can make this easier.

1. MeSH Browser: We can use the MeSH Browser to insert terms into the search as described above. This avoids any problems with spelling or syntax.

2. Stepwise approach: We can break our search into different parts and combine them at the end. In a classical EBM search we will have several alternative terms in each column of the PICO question that need to be linked using the "OR" operator. We also have 3 or 4 columns, across which we need to use "AND" as a linking operator. It is easy to see the potential for an unmanageable number of brackets if we try to phrase this in one big question.

We can start by searching the terms in one column of the P I C O question, linked by "OR". Using the "Search" button we can see how many articles this would retrieve. We then clear the search box and search the terms in the second column, again linked by "OR" and using the "Search" button. We do the same for the third and fourth column. By clicking on "History" we can now see a list of each of the 4 previous searches, numbered #1 to #4. The next step is to enter the following string into the search box: #1 AND #2 AND #3 AND #4. Cochrane then combines the results of each search and retrieves only articles that contain MeSH terms from all 4 columns.

NB: The indexing is not always perfect. Therefore it is often useful to browse through the results of different combinations (eg #1 AND #2) so as not to exclude important articles that were not comprehensively indexed. If the article has not been indexed with MeSH terms from all 4 columns of your search, then you will not retrieve that article.


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