Support : Publications : Chronolog Archives : January/February 2004

From the Experts...

Thesaurus Mappin in MEDLINE® and EMBASE®

Thesaurus mapping in MEDLINE and EMBASE lets you retrieve the most suitable controlled language from a freetext search. But there may be instances in which using the thesaurus "Enter a Term" option is preferable.

The essential difference between Thesaurus mapping and using the MEDLINE or EMBASE "Enter a Term" option is that the mapping feature analyzes the documents searched and ranks the most relevant descriptors accordingly. The main benefit of mapping is that you can link a freetext term to the most relevant controlled vocabulary descriptor from MeSH or EMTREE. For example, if you search for "MMR Vaccine" in freetext and map these terms, you will retrieve "Measles, Mumps and Rubella Vaccine" from the Thesaurus list as well as "Mumps Vaccine," "Measles Vaccine," "Rubella Vaccine" and "Autistic Disorder." This is because the frequency of these descriptors in the actual articles is mirrored in the retrieved list of Thesaurus terms.

The mapping feature is especially useful when terms entered directly into MeSH do not retrieve relevant hits (e.g., lung cancer in MEDLINE is not a MeSH term and retrieves 0). If, however, you map the term "lung cancer," you will retrieve "lung neoplasms" at the top of the list of mapped terms. This is because Dialog DataStar has mapped the descriptors in the documents and presented them in order of relevance. Once you have obtained your preferred term, you can use the same features that are available in the thesaurus proper: EXPLODE, Major and Subheadings. Note that Mapping also accommodates any date restrictions imposed on a search. If you search over three months, you will get fewer results than if you search over 12 months, and this will be reflected in the number of titles obtained from searching the mapped thesaurus list.

The powerful drug indexing in EMBASE lets you locate the generic (INN) names of drugs, "Sildenafil" for "Viagra," for example. Using Thesaurus mapping on a drug name retrieves the generic name, but there are instances in which the condition the drug is used to treat represents the first item on the list. For example, "Retrovir," when mapped, retrieves HIV. Zidovudine, the generic name for Retrovir, appears further down the list of thesaurus terms, along with several other comparative HIV drugs. You may not know that this is the correct name. By using "Emtree Enter a Term," you are guaranteed to retrieve the generic name for Retrovir exclusively. You also don't have to worry about any date restrictions imposed on the search because using the thesaurus directly represents the content of the entire database.

Another instance where Thesaurus mapping may be limited is in common phrases such as "treatment outcomes." Here you may not get the desired result because the term is too broad. If, however, you go into the thesaurus "Enter a term" section, you can often find these terms because you are looking up the term directly, as opposed to analyzing the documents retrieved.

So, Thesaurus mapping gives the best of both worlds: you can search in freetext and retrieve the relevant descriptors but the thesaurus can still be used when a) you are familiar with MeSH or EMTREE terminology and you want to verify a descriptor; or b) you have not obtained the desired result from a mapped list and want to check that the term is still available in the Thesaurus.

Richard Levy
Training Consultant
United Kingdom

MEDLINE Notice

We recommend that all MEDLINE (Files 154, 155/MEZZ, MEDL) customers regularly refer to the database banners in these files for the latest status on the updating of "Completed" records and the 2004 reload. Alternatively, contact the Knowledge Center for help.

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