Free AccessLetter to the EditorAccuracy of linear intraoral measurements using cone beam CT and multidetector CT: methodological mistake: Author responseR PatcasR PatcasSearch for more papers by this authorPublished Online:28 Jan 2014https://doi.org/10.1259/dmfr.20130062SectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail AboutWe were pleased to receive the letter from Sabour and Kermani1 which addresses our article “Accuracy of linear intraoral measurements using cone beam CT and multidetector CT: a tale of two CTs”.2We consider their comments to be helpful to readers because they broaden the discussion on the proper statistical approach to be used to validate accuracy. In brief, Sabour and Kermani caution not to confuse the assessment of validity (i.e. accuracy) with reliability (i.e. repeatability or reproducibility). We share their concern and have likewise mentioned elsewhere3 that many studies evaluating imaging accuracy suffer from unsuitable statistical evaluations. Thus, we took care to address the questions of validity and reliability in our article separately, each with an appropriate statistical approach.We are, however, surprised at Sabour and Kermani’s comment on the assessment of accuracy. In their letter, they suggest sensitivity, specificity, positive and negative predictive values, likelihood ratios and odds ratio as tests to evaluate the validity (accuracy) of a method compared with a gold standard. Although inherently correct for categorical data, these comments fail to be relevant to our study, because all these analyses are inapplicable for continuous values such as linear measurements.So, what would be the best way to evaluate the validity of linear measurements? When trying to assess the degree of agreement, the correct statistical approach is not obvious. To identify whether two methods of measurement are interchangeable, we need to know by how much one method is likely to differ from the other.4 The simplest and most popular approach5 is the Bland–Altman method,6 consisting of plotting the difference between the two measurements against the mean of the two measurements and establishing the limits of agreement (LOA).7 Provided the assumptions of uniform mean and standard deviation are met, the Bland–Altman plot with its LOA can be carried out by anyone with basic statistical knowledge, offering results that are easy to interpret in a meaningful way.8Sabour and Kermani charge us by writing that “the common practice for assessing validity (accuracy) is to apply well-known statistical tests, and it is unclear why the authors did not consider employing such practice.” The original publication of Bland and Altman6 has by now been cited well over 25 000 times. We wonder how much more well known a method could be?References1 Sabour S, Kermani H. Accuracy of linear intraoral measurements using cone beam CT and multidetector CT: methodological mistake. Dentomaxillofac Radiol 2013; 42: 20130048. Link ISI, Google Scholar2 Patcas R, Markic G, Muller L, Ullrich O, Peltomaki T, Kellenberger CJ, et al.. Accuracy of linear intraoral measurements using cone beam CT and multidetector CT: a tale of two CTs. Dentomaxillofac Radiol 2012; 41: 637–44. doi: 10.1259/dmfr/21152480. Link ISI, Google Scholar3 Patcas R, Muller L, Ullrich O, Peltomaki T. Accuracy of cone-beam computed tomography at different resolutions assessed on the bony covering of the mandibular anterior teeth. Am J Orthod Dentofacial Orthop 2012; 141: 41–50. doi: 10.1016/j.ajodo.2011.06.034. Crossref Medline ISI, Google Scholar4 Bland JM, Altman DG. Measuring agreement in method comparison studies. Stat Methods Med Res 1999; 8: 135–160. Crossref Medline ISI, Google Scholar5 Ludbrook J. Statistics in biomedical laboratory and clinical science: applications, issues and pitfalls. Med Princ Pract 2008; 17: 1–13. doi: 10.1159/000109583. Crossref Medline ISI, Google Scholar6 Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307–310. Crossref Medline ISI, Google Scholar7 Bland JM, Altman DG. Comparing methods of measurement: why plotting difference against standard method is misleading. Lancet 1995; 346: 1085–1087. Crossref Medline ISI, Google Scholar8 Bland JM, Altman DG. Applying the right statistics: analyses of measurement studies. Ultrasound Obstet Gynecol 2003; 22: 85–93. doi: 10.1002/uog.122. Crossref Medline ISI, Google Scholar Previous article Next article FiguresReferencesRelatedDetails Volume 42, Issue 4April 2013 © 2013 The Authors History Published onlineJanuary 28,2014 Metrics Download PDF