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Intraclass correlation – A discussion and demonstration of basic features

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  • David Liljequist
  • Britt Elfving
  • Kirsti Skavberg Roaldsen

Abstract

A re-analysis of intraclass correlation (ICC) theory is presented together with Monte Carlo simulations of ICC probability distributions. A partly revised and simplified theory of the single-score ICC is obtained, together with an alternative and simple recipe for its use in reliability studies. Our main, practical conclusion is that in the analysis of a reliability study it is neither necessary nor convenient to start from an initial choice of a specified statistical model. Rather, one may impartially use all three single-score ICC formulas. A near equality of the three ICC values indicates the absence of bias (systematic error), in which case the classical (one-way random) ICC may be used. A consistency ICC larger than absolute agreement ICC indicates the presence of non-negligible bias; if so, classical ICC is invalid and misleading. An F-test may be used to confirm whether biases are present. From the resulting model (without or with bias) variances and confidence intervals may then be calculated. In presence of bias, both absolute agreement ICC and consistency ICC should be reported, since they give different and complementary information about the reliability of the method. A clinical example with data from the literature is given.

Suggested Citation

  • David Liljequist & Britt Elfving & Kirsti Skavberg Roaldsen, 2019. "Intraclass correlation – A discussion and demonstration of basic features," PLOS ONE, Public Library of Science, vol. 14(7), pages 1-35, July.
    • Handle: RePEc:plo:pone00:0219854
    DOI: 10.1371/journal.pone.0219854
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    References listed on IDEAS

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    1. Tony Bohman & Matthias Tegern & Alexandra Halvarsson & Lisbet Broman & Helena Larsson, 2018. "Reliability and agreement of the IsoKai isokinetic lift test – A test used for admission to the Swedish Armed Forces," PLOS ONE, Public Library of Science, vol. 13(12), pages 1-13, December.
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    Cited by:

    1. Ajax Persaud & Javid Zare, 2023. "Institutional varieties, governance quality, and firm‐level innovation in emerging economies: Case of India," Growth and Change, Wiley Blackwell, vol. 54(1), pages 234-259, March.
    2. Genis Cardona & Noelia Esterich, 2019. "Awareness of treatment: A source of bias in subjective grading of ocular complications," PLOS ONE, Public Library of Science, vol. 14(12), pages 1-9, December.
    3. M. Haas & S. Scheibe & E. El Khawli & M. Künzi & A. Ihle & N. Ballhausen & D. Framorando & M. Kliegel & S. Zuber, 2022. "Online assessment of cognitive functioning across the adult lifespan using the eCOGTEL: a reliable alternative to laboratory testing," European Journal of Ageing, Springer, vol. 19(3), pages 609-619, September.
    4. Begoña Cueto & Patricia Suárez & Matías Mayor, 2021. "Effects of human capital and regional context on entrepreneurial survival," The Annals of Regional Science, Springer;Western Regional Science Association, vol. 66(2), pages 331-357, April.
    5. Kirsti Skavberg Roaldsen & Alexandra Halvarsson, 2019. "Reliability of the Swedish version of the Evidence-Based Practice Attitude Scale assessing physiotherapist’s attitudes to implementation of evidence-based practice," PLOS ONE, Public Library of Science, vol. 14(11), pages 1-10, November.

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