Abstract
Background:
Cohen’s kappa is a statistic that estimates interobserver agreement. It was originally introduced to help develop diagnostic tests. Interpretative readings of 2 observers, for example, of a mammogram or other imaging, were compared at a single point in time. It is known that kappa depends on the prevalence of disease and that, therefore, kappas across different settings are hard to compare.
Methods:
Using simulation, we examine an analogous situation, not previously described, that occurs in clinical trials where sequential measurements are obtained to evaluate disease progression or clinical improvement over time.
Results:
We show that weighted kappa, used for multilevel outcomes, changes during the trial even if we keep the performance of the observer constant.
Conclusions:
Kappa and closely related measures can therefore only be used with great difficulty, if at all, in quality assurance in clinical trials.
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Reeve, R., Gottlieb, K. Sequentially Determined Measures of Interobserver Agreement (Kappa) in Clinical Trials May Vary Independent of Changes in Observer Performance. Ther Innov Regul Sci 54, 681–686 (2020). https://doi.org/10.1007/s43441-019-00102-5
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DOI: https://doi.org/10.1007/s43441-019-00102-5