Categorical skill metrics such as the False Alarm Ratio (FAR), the Probability of Detection (POD), the Critical Success Index (CSI), and Equitable Threat Score (ETS) are also relevant for some forecasting applications.
Skill is often, but not exclusively, expressed as the relative representation that compares the performance of a particular forecast prediction to that of a reference, benchmark prediction—a formulation called a 'Skill Score'.
Forecasting skill metric and score calculations should be made over a large enough sample of forecast-observation pairs to be statistically robust.
A sample could also pool forecast-observation pairs across space, for a prediction made on a single date, as in the forecast of a weather event that is verified at many locations.
[6] A popular textbook and reference that discusses forecast skill is Statistical Methods in the Atmospheric Sciences.