Rationale and objectives: The aim of the study is to develop a permutation test to compare receiver operating characteristic (ROC) curves of two diagnostic modalities in a multireader paired design.
Materials and methods: A statistical test for comparing two diagnostic modalities is developed based on all possible exchanges of the set of reader-ratings between the two modalities. An exact permutation test is formed by determining the frequency of the most extreme values of the statistic estimating the average difference in the areas under the ROC curves (AUCs). An asymptotic version of the test is constructed by obtaining the exact permutation variance and appealing to the asymptotic normality of the nonparametric estimator of the average difference in areas. Computer simulations were conducted to validate the type I error for small sample sizes.
Results: The new test provides a permutation approach for comparing ROC curves in a multireader paired-design setting in which effects of the readers are considered to be fixed. The type I error of the asymptotic test is close to the true value, even for samples as small as 20 normal and 20 abnormal cases. The test is designed to be sensitive to alternatives in which the AUCs of the two diagnostic modalities differ.
Conclusions: The proposed test provides a powerful method for comparing two diagnostic modalities in a multireader paired-study design when the primary interest is to detect difference in average AUCs.