## 432: ROC Graphs

The ROC graphs are constructed using a set of probabilistic forecasts over time and/or space. The ROC statistics are calculated using predictions for all gridpoints / stations / series. The probabilistic forecasts are binned to the nearest 10% (in accordance with the WMO's Standardized Verification System for Long-Range Forecasts (SVSLRF) ), although there is an option to bin to the nearest 5% ( Options ~ Verification Settings ). Results are shown separately for the three categories, and the areas beneath the graphs, calculated using the trapezium rule, are shown. Note that the ROC areas will not necessarily agree with the 2AFC scores for the individual categories shown on the Probabilistic Scores page because the areas are calculated using binned forecast probabilities, whereas the scores page shows scores for continuous probabilities.

The ROC statistics can be saved by right-clicking on the graphs. The graph itself can be saved as a graphics file by right-clicking anywhere in the child window and selecting Export from the pop-up menu. A default name is given to the graphics file, but this name can be changed using the browse button. The image quality for all the graphics formats can be improved by increasing the size of the image (see Options ~ Graphics ~ Graph Scaling ).