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Beware of word truncation in PubMed: unexpected problems and potential solutions
  1. Rafael Vieira1,
  2. Bernardo Sousa-Pinto2,3,
  3. Luís Figueira4,5
  1. 1 Department of Ophthalmology, University Hospital Center of São João, Porto, Portugal
  2. 2 MEDCIDS—Department of Community Medicine, Information and Health Decision Sciences, Faculty of Medicine, University of Porto, Porto, Portugal
  3. 3 CINTESIS—Center for Health Technology and Services Research, Faculty of Medicine, University of Porto, Porto, Portugal
  4. 4 Unit of Pharmacology and Therapeutics, Department of Biomedicine, Faculty of Medicine, University of Porto, Porto, Portugal
  5. 5 Department of Ophthalmology, University Hospitals Center of São João, Porto, Portugal
  1. Correspondence to Dr Rafael Vieira, University Hospital Center of São João, Porto, Portugal; mail{at}

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PubMed allows truncation of a given term by using an asterisk (*).1 Its purpose is to retrieve the first 600 words containing the part of the word preceding the asterisk, and it is a recommended practice when building the queries to be used in systematic reviews.2 However, unawareness on how truncation is enforced—particularly when searching for expressions with more than one word—can result in obtaining a lower number of results than what would be intuitively expected.

PubMed documentation explicitly states that “truncation bypasses Automatic Term Mapping and automatic explosion”,1 so that a truncated search can return less …

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  • Contributors RV, BS-P and LF contributed to the design and implementation of the research. RV and BS-P contributed to the analysis of the results and to the writing of the manuscript. RV, BS-P and LF reviewed and approved the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.