Skill Kit: Truncation in PubMed®

Editor's note: Refer to the PubMed User Guide for the most up-to-date instruction.

a truncation search feature provides the ability to search for variant words or spellings. Sometimes called a wildcard, this is a standard search feature found on many search engines; however, different search engines may use a different truncation or wild card symbol. New searchers may overlook this feature, while more experienced users may forget which truncation symbol is used on different search engines. But for those searchers trying to increase their searching knowledge and expertise, truncation can be a useful, though tricky feature.

In PubMed, the question may really be should you use truncation or not? The PubMed truncation feature provides only a right-hand truncation function. This means that PubMed will look for variations in phrasing/spelling to the right of the truncation symbol. And using the PubMed truncation feature also has some specific consequences:

• Automatic Term Mapping (ATM) is turned off;
• The truncation function looks for only the first 600 variations, so the search could be incomplete;
• Truncation can cause a search to time out if an excessive number of variants are generated.
• Truncation can cause lengthy and confusing error messages for My NCBI updates.

In PubMed, the truncation symbol is the asterisk (*), which can be used at the end of a word to search for all terms that begin with that basic word root. A search for variations of the term photosynthesis could be done with a truncation search for photosynth*, and include the following variations:

photosynth	photosynthesised	photosynthetical
photosynthate	photosynthesising	photosynthetically
photosynthates	photosynthesize	photosyntheticus
photosyntheic	photosynthesized	photosynthetiques
photosyntheis	photosynthesizer	photosynthetis
photosynthese	photosynthesizers	photosynthetising
photosynthese'	photosynthesizing	photosynthetizing
photosyntheses	photosynthetic	photosynthic
photosynthesis	photosynthetic'	photosynthse
photosynthesis'	photosynthetica

Clicking on the Details tab allows you to see what has been searched, based on the use of the truncation symbol. This search is a good example of not truncating a word or word-stem too soon. If the truncation symbol had been used after photo*, not only would the user have retrieved inappropriate matches (such as photography), but the search would have been limited to the first 600 variants. It is also possible that the search system could time out due to the large number of variant words that could start with photo. This function only works for a single word or word stem, not for multi-word phrases (e.g., heart* retrieves heart, hearts, heart/diagnosis, etc., but not heart attack). The word-stemming stops once the search system encounters a space. However, if the truncation symbol is used at the end of a multi-word phrase, it will initiate a phrase search (e.g., germ cell line* retrieves germ cell line, germ cell lines, and germ cell lineage).

Because ATM is turned off when using truncation, it is not a regularly recommended search feature. Truncation should be used carefully. It is probably best used when doing a specified tagged search, such as title or text word.

More details about using a truncation search can be found in PubMed Help.

Skill Kit: Truncation in PubMed. NLM Tech Bull. 2006 Jan-Feb;(348):e7.