Comparison of Two Diagnostic Test Procedures Using Modified Wilcoxon Signed Rank Test

U.M. Okeh and I. Onyeagu Sidney

Background and Objectives: Receiver Operating Characteristic (ROC) analysis has been used as a popular technique of comparing the performance of two paired diagnostic tests data while the Area under the Curve (AUC) summarizes the overall activities between two ROC curves. This study was aimed at assessing a difference in the AUCs of paired data where each non-diseased and diseased subject are both subjected to 2 diagnostic test procedures as well as to tackle the problem of exchangeability of the labels between two diagnostic tests within subject which characterizes previous studies. Materials and Methods: A modified Wilcoxon Signed-Rank Test to accommodate the presence of tied absolute values of differences for assessing a difference in the AUCs in a continuous matched pair of data was proposed. A real data was analyzed to compare the proposed test and that of standard test as well as the 2 diagnostic tests. Results: Test reveals that the p-values for 2 h 70 g OGTT and 2 h 100 g OGTT for the non-diseased subjects are, respectively 0.6124 and 0.8975 while that of diseased subjects are, respectively 0.6345 and 0.8765. The estimates of AUC₁ and AUC₂ for diagnostic tests are 0.668 and 0.887, respectively. Conclusion: Result showed that the proposed test is more powerful than the standard test. Also 2 h 100 g OGTT diagnostic test is superior to 2 h 70 g OGTT diagnostic test at a time that the specificity is greater than 0.7.

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