Journal
THERAPEUTIC INNOVATION & REGULATORY SCIENCE
Volume -, Issue -, Pages -Publisher
SPRINGER HEIDELBERG
DOI: 10.1177/2168479019874059
Keywords
clinical trials; interobserver agreement; Cohen kappa; repeated measures; biased estimator; simulation; central reading
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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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