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  1. S V Kemp,
  2. P L Shah
  1. Royal Brompton Hospital, London, UK
  1. Correspondence to P L Shah, Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK; pallav.shah{at}

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We agree with Drs Slade and Slade that success in endobronchial ultrasound-guided transbronchial needle aspiration relies on many factors other than the skill of the actual bronchoscopist and, as such, the term ‘operator’ may have been misleading. Nevertheless, the operator is going to have the greatest bearing on the results obtained. The article1 was intended to highlight the need for more accurate methods of assessment of competency in any given task or procedure, using endobronchial ultrasound-guided transbronchial needle aspiration only as an example.

I am sure Drs Slade and Slade recognise that, as in medicine, there are valid alternative interpretations for data. In the referenced paper by Bolsin and Colson,2 the discussion of Kestin's Cusum plots states that ‘acceptable performance will be denoted on this format by a Cusum line which is roughly horizontal or down-sloping’—that is, a line crossing multiple decision intervals from above is not required to say that performance is acceptable. While a horizontal line does not indicate learning per se, this may not necessarily be an appropriate objective in more experienced practitioners/centres where the focus is on monitoring ongoing competence.

The interpretation of statistical methods is always open to differences, but there is little doubt that Cusum analysis allows the effective monitoring of practices and procedures and, when a change in outcomes is observed (whatever predetermined criteria are used), we as clinicians should reflect on our practice in order to determine which aspects of that practice require attention.



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  • Competing interests None.

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

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