Letter to the Editor | Published:

Response to Sabour

Pediatric Research volume 82, page 177 (2017) | Download Citation

To the Editor: We read the concerns of Mr Sabour (1) with some interest. In our study (2), we essentially analyzed the agreement of body-scanner measurements between three repetitive assessments by the same observer (intra-observer reliability) and between body-scanner measurements and corresponding measurements of classical anthropometry if available (validity).

All analyzed measurements are quantitative. Except intra/interclass correlation coefficients, all statistical measures proposed by Sabour are designed for binary/categorical variables and cannot be applied in our situation. Moreover, proposed measures like sensitivity, specificity, etc, have nothing to do with agreement.

Intra-class correlation coefficient cannot be used in our situation either, because our data are paired. We used concordance correlation coefficients (CCCs) to assess agreement in our study. This measure is maximal if there are no biases, no differences in the variances, and if there exist perfect correlations between two or more paired measurement series. The author also proposed interclass correlation as an alternative measure here, which, however, is less stringent than the CCC.

The concerns expressed by the author in paragraph 3 of his letter are obscure. There is no recognizable concept of “concordance and discordance cells” in our situation. Concordance is quantitatively assessed in our situation and not by tables. The author claims that CCC<0.5 is like “Flipping a coin.” Again, it appears that the author mixed up concepts and we would like to refer to the literature (3, 4, 5) where the statistical properties of the CCC are explained in detail. A short explanation is given in our Methods section.

In the letter by Sabour, our research paper was cited as follows: “Based on their results, intra-observer reliability of both techniques is “excellent” (OCCC≥0.9). However, neck and thigh circumference a “good” (CCC≥0.7) and head circumference a “low” (CCC<0.5; Flipping a coin!) degree of concordance over the complete study population.” This does not correctly represent the content of our paper. The statements regarding neck, thigh, and head circumference are taken from our validity analysis—i.e., agreement of conventional with laser-based anthropometry—and not from the intra-observer reliability analysis as claimed by the author.

In summary, we are confident that we used appropriate statistics for our analyses and that conclusions thereon are correct.

References

  1. 1.

    Sabour S. Validity and reliability of three-dimensional scanning compared to conventional anthropometry for children and adolescents: methodological mistake. Pediatr Res 2017 (e-pub ahead of print 31 May 2017)..

  2. 2.

    Glock F, Vogel M, Naumann S et al. Validity and intraobserver reliability of three-dimensional scanning compared with conventional anthropometry for children and adolescents from a population-based cohort study. Pediatr Res 2017;81:736–744.

  3. 3.

    . A concordance correlation coefficient to evaluate reproducibility. Biometrics 1989;45:255–68.

  4. 4.

    . A note on the concordance correlation coefficient. Biometrics 2000;56:324–25.

  5. 5.

    , , . Overall concordance correlation coefficient for evaluating agreement among multiple observers. Biometrics 2002;58:1020–27.

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Acknowledgements

This publication is supported by LIFE—Leipzig Research Centre for Civilization Diseases. LIFE is supported by the European Union, by the European Regional Development Fund (ERDF), and by funds from the Free State of Saxony in the context of the excellence initiative.

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Affiliations

  1. Hospital for Children and Adolescents—Centre for Pediatric Research, Leipzig University, Leipzig, Germany

    • Fabian Glock
    •  & Wieland Kiess
  2. Institute for Medical Informatics, Statistics and Epidemiology, Leipzig University, Leipzig, Germany

    • Markus Scholz
    •  & Andreas Kuehnapfel

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The authors declare no conflict of interest.

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Correspondence to Wieland Kiess.

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DOI

https://doi.org/10.1038/pr.2017.76