Comparative performance of two methods that assess the quality of international normalized ratio measures

Objectives: Two methods, Petersen's error grid analysis and Shermock's method to detect clinically important differences, were recently developed to advance the assessment of analytic performance of point-of-care INR devices. Both methods predict when alternate INR measures lead to different clinical decisions. Our goal was to compare their performance characteristics. Design and methods: Performance characteristics were assessed by comparing the models' predictions to clinical decisions that were directly measured in a previous experiment. Results: Shermock's method (82% of predictions correct) demonstrated superior predictive performance compared with the error grid analysis (75% of predictions correct, p = 0.008). Shermock's method was particularly superior at identifying the clinical decisions that actually disagreed (79% for Shermock's method vs. 47% for error grid). Consequently, Shermock's method was superior at identifying a POC device with poor performance (79% accuracy vs. 70%, p = 0.006). Conclusion: Shermock's method had superior performance characteristics and should be integrated into analytic strategies to assess POC INR devices.