- Email: [email protected]
Reply to: Reproducibility of semi-automatic coronary plaque quantification in coronary CT angiography with sub-mSv radiation dose; common mistakes
Journal of Cardiovascular Computed Tomography 10 (2016) e23
Contents lists available at ScienceDirect
Journal of Cardiovascular Computed Tomography journal homepage: www.JournalofCardiovascularCT.com
Letter to the Editor
Reply to: Reproducibility of semi-automatic coronary plaque quantification in coronary CT angiography with sub-mSv radiation dose; common mistakes
Dear Author,
References
Thank you very much for your interest in our study concerning the reproducibility of semi-automatic plaque quantification in coronary CT angiography with sub-mSv radiation dose.1 First of all, we would like to thank you for having read our paper, and for taking the time to comment on our analyses. We agree that correlation coefficients in terms of reproducibility analyses have shortcomings that are important to be aware of. As you point out, any correlation coefficient depends on the variation within and between subjects, and furthermore, does not fully take into account a possible shift in location or scale; if measure one was consistently half of measurement two, the correlation coefficient would still be high. Intra-class correlation coefficients share this weakness too. We did not perform Intra-class Correlation Coefficient analysis in our study, due to these and other weaknesses, which have been pointed out previously by Müller and Büttner2 and Bland and Altman.3 In reports of test-retest reproducibility, BlandAltman analyses and repeatability coefficients are considered more appropriate.4e7 Importantly, therefore, we reported the scatterplots and performed Bland-Altman analyses that are commonly regarded as a valid standardized method to measure reproducibility for clinical measurements6; it shows the difference, systematic bias as well as 95% limits of agreement between the two measurements, in their corresponding units. One of the additional advantages of the Bland-Altman method is its wide distribution in the research community so that comparability to recent or further studies can be easily achieved. Along with Bland-Altman analysis, we also reported the repeatability coefficients that have been shown to be a reliable method to measure test-retest reliability.7 The mean differences, standard deviations with p-values were also presented to provide a complete descriptive picture of the data.
1. Øvrehus KA, Schuhbaeck A, Marwan M, et al. Reproducibility of semi-automatic coronary plaque quantification in coronary CT angiography with sub-mSv radiation dose. J Cardiovasc Comput Tomogr. 2016;10:114e120. 2. Müller R, Büttner P. A critical discussion of intraclass correlation coefficients. Stat Med. 1994;13:2465e2476. 3. Bland JM, Altman DG. A note on the use of the intraclass correlation coefficient in the evaluation of agreement between two methods of measurement. Comput Biol Med. 1990:337e340. L, Brorson S, et al. Guidelines for reporting reliability and 4. Kottner J, Audige agreement studies (GRRAS). J Clin Epidemiol. 2011;64:96e106. 5. de Vet HC, Terwee CB, Knol DL, Bouter LM, et al. When to use agreement versus reliability measures. J Clin Epidemiol. 2006;59:1033e1039. 6. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307e310. 7. Vaz S, Falkmer T, Passmore AE, Parsons R, Andreou P. The case for using the repeatability coefficient when calculating testeretest reliability. PLoS One. 2013;8(9):e73990. http://dx.doi.org/10.1371/journal.pone.0073990.
Kristian Altern Øvrehus* Aarhus University Hospital, Department of Cardiology, Denmark Lillebaelt Hospital Vejle, Department of Cardiology, Denmark Odense University Hospital, Department of Cardiology, Denmark Damini Dey Cedars Sinai Medical Center, Los Angeles, USA *
Corresponding author. Aarhus University Hospital, Department of Cardiology, Denmark. E-mail address: [email protected] (K.A. Øvrehus).
Conflict of interests The authors have no conflict of interests.
DOI of original article: http://dx.doi.org/10.1016/j.jcct.2015.11.003. http://dx.doi.org/10.1016/j.jcct.2016.07.001 1934-5925/© 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.
30 June 2016 Available online 20 August 2016
Contents lists available at ScienceDirect
Journal of Cardiovascular Computed Tomography journal homepage: www.JournalofCardiovascularCT.com
Letter to the Editor
Reply to: Reproducibility of semi-automatic coronary plaque quantification in coronary CT angiography with sub-mSv radiation dose; common mistakes
Dear Author,
References
Thank you very much for your interest in our study concerning the reproducibility of semi-automatic plaque quantification in coronary CT angiography with sub-mSv radiation dose.1 First of all, we would like to thank you for having read our paper, and for taking the time to comment on our analyses. We agree that correlation coefficients in terms of reproducibility analyses have shortcomings that are important to be aware of. As you point out, any correlation coefficient depends on the variation within and between subjects, and furthermore, does not fully take into account a possible shift in location or scale; if measure one was consistently half of measurement two, the correlation coefficient would still be high. Intra-class correlation coefficients share this weakness too. We did not perform Intra-class Correlation Coefficient analysis in our study, due to these and other weaknesses, which have been pointed out previously by Müller and Büttner2 and Bland and Altman.3 In reports of test-retest reproducibility, BlandAltman analyses and repeatability coefficients are considered more appropriate.4e7 Importantly, therefore, we reported the scatterplots and performed Bland-Altman analyses that are commonly regarded as a valid standardized method to measure reproducibility for clinical measurements6; it shows the difference, systematic bias as well as 95% limits of agreement between the two measurements, in their corresponding units. One of the additional advantages of the Bland-Altman method is its wide distribution in the research community so that comparability to recent or further studies can be easily achieved. Along with Bland-Altman analysis, we also reported the repeatability coefficients that have been shown to be a reliable method to measure test-retest reliability.7 The mean differences, standard deviations with p-values were also presented to provide a complete descriptive picture of the data.
1. Øvrehus KA, Schuhbaeck A, Marwan M, et al. Reproducibility of semi-automatic coronary plaque quantification in coronary CT angiography with sub-mSv radiation dose. J Cardiovasc Comput Tomogr. 2016;10:114e120. 2. Müller R, Büttner P. A critical discussion of intraclass correlation coefficients. Stat Med. 1994;13:2465e2476. 3. Bland JM, Altman DG. A note on the use of the intraclass correlation coefficient in the evaluation of agreement between two methods of measurement. Comput Biol Med. 1990:337e340. L, Brorson S, et al. Guidelines for reporting reliability and 4. Kottner J, Audige agreement studies (GRRAS). J Clin Epidemiol. 2011;64:96e106. 5. de Vet HC, Terwee CB, Knol DL, Bouter LM, et al. When to use agreement versus reliability measures. J Clin Epidemiol. 2006;59:1033e1039. 6. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307e310. 7. Vaz S, Falkmer T, Passmore AE, Parsons R, Andreou P. The case for using the repeatability coefficient when calculating testeretest reliability. PLoS One. 2013;8(9):e73990. http://dx.doi.org/10.1371/journal.pone.0073990.
Kristian Altern Øvrehus* Aarhus University Hospital, Department of Cardiology, Denmark Lillebaelt Hospital Vejle, Department of Cardiology, Denmark Odense University Hospital, Department of Cardiology, Denmark Damini Dey Cedars Sinai Medical Center, Los Angeles, USA *
Corresponding author. Aarhus University Hospital, Department of Cardiology, Denmark. E-mail address: [email protected] (K.A. Øvrehus).
Conflict of interests The authors have no conflict of interests.
DOI of original article: http://dx.doi.org/10.1016/j.jcct.2015.11.003. http://dx.doi.org/10.1016/j.jcct.2016.07.001 1934-5925/© 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.
30 June 2016 Available online 20 August 2016