What is plotted on the Y-axis of a Receiver Operating Characteristic (ROC) curve?

In a Receiver Operating Characteristic (ROC) curve, the Y-axis represents the true positive rate, which is also known as sensitivity or recall. This metric indicates the proportion of actual positives that are correctly identified by the test or model. In other words, it showcases how effectively a test distinguishes between the positive and negative cases.

Plotting the true positive rate on the Y-axis allows for a visual representation of the performance of a diagnostic test across various threshold levels. As the threshold for classifying a positive result adjusts, the true positive rate will change, reflecting the trade-off between sensitivity and specificity. A higher true positive rate indicates that the test is effectively identifying more of the actual positive cases, thereby demonstrating a better performance overall.

When examining an ROC curve, understanding the true positive rate's position on the Y-axis allows practitioners to evaluate and compare the diagnostic capabilities of different tests or classifiers in distinguishing between health states, ultimately aiding in clinical decision-making.