The truncation confusion

The truncation confusion

“Search using keywords”.

This is what most guides / teachers tell students when they want them to do a literature search. Keywords are usually the important words from one’s research question, that one uses to perform a search. For a research topic like: – “Long-term risk of pneumothorax in asthmatic patients”, the keywords used to search for literature would be – pneumothorax and asthma.

In databases like PubMed, one could search these as thesaurus terms (Mesh terms) to get the most relevant results. The search strategy would be :

Asthma[mesh] AND pneumothorax[mesh]

But, when one is doing an exhaustive search – in contexts like authoring a systematic review, one needs to also search for these keywords – as terms that appear in the title and abstract. Different authors may use different forms of these words. For asthma, an author may use asthmas, asthmatic, asthmatics or asthmaticus.

If we search with the keyword – asthma – and if an author has used the word asthmatic in the title and abstract, we would not retrieve this item.

And so, we need to use a truncation symbol to ensure that we retrieve all variations of the word. We need to search:


When we search asthma*[tiab], we ask the search engine to search for the presence of any of these words: asthma, asthmas, asthmatic, asthmatics or asthmaticus – in the title and in the abstract

That seems easy. Where is the confusion?

I recently realized that quite a few people who go through my courses, believe that they need to truncate a word if they want different words to follow their search term.

And so – they type asthmatic*[tiab], believing they need to do this, to retrieve – asthmatic children, asthmatic men, asthmatic women and more!!

Asthmatic* – retrieves items that contain the words asthmatic or asthmatics, or asthmaticus. The words children, men, women etc, if present will automatically appear in the results.

Do remember these rules while truncating any search term in PubMed:

  1. The truncation symbol is just for variations in a single word, and NOT for a group of words. Use the symbol * for words where there is a possibility of the presence of  different letters at the end. eg – asthma*, diabet* etc
  2. Do not use the symbol at the end of a plural – eg – do not search for asthmatics* – there are no words that have any letter after asthmatics
  3. Do not use the symbol when you tag your search term with [mesh]. When you wish to tag a search term with [mesh], the term MUST be present in the mesh database

Note: Other databases have many other truncation symbols like #,? and more.  Some permit a truncation symbol at the beginning or middle of words too. One needs to learn the use of these symbols, from the help files of those databases.

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