What is a ROC curve used for?

A ROC curve, or Receiver Operating Characteristic curve, is primarily used as a graphical representation of a model's performance, specifically in the context of binary classification problems. It illustrates the trade-off between the true positive rate (sensitivity) and the false positive rate (1-specificity) as the threshold for classifying observations into classes is varied.

By plotting these rates on the y-axis and x-axis respectively, the ROC curve provides a visual tool to evaluate how well a model distinguishes between the two classes. A model that perfectly classifies all positive and negative instances would achieve a point in the upper left corner of the graph, indicating 100% sensitivity and 0% false positive rate. The area under the ROC curve (AUC) is also a valuable metric derived from this representation, where a higher area indicates better model performance.

The other options do not capture the specific purpose of a ROC curve. While it indirectly relates to model accuracy, the ROC curve itself does not measure accuracy directly; rather, it focuses on the balance between true and false classifications. It is also distinct from methods used in time series analysis and is not a tool for visualizing training data.