The false alarm ratio is the fraction of the forecasts of the event associated with non-occurrences, as the name implies and is defined by:

FAR = (false alarms) / (number of forecasts of the event)

The FAR can be controlled by deliberately underforecasting the event; such a strategy risks increasing the number of missed events, which is not considered in the FAR. For this reason, the POD and the FAR should both be considered for a better understanding of the performance of the forecast.

The post-agreement is the complement of the FAR:

PAG = (hits) / (number of forecasts of the event)

The PAG is the fraction of forecasts which were correct, and is not widely used.

The False alarm rate (F) is given by:

F = (false alarms) / (number of observations of the non-event)

Thus, F is the fraction of non-events which were forecast as false alarms. The false alarm rate is sometimes called the probability of false detection (POFD). In that sense, it is akin to false positives on a medical test, or on an X-ray. Along with the hit rate, the false alarm rate is used in the relative operating characteristic (ROC) calculations and is related to the Hanssen-Kuipers skill score, described in the next unit. It is not otherwise widely used.

Question: Determine the false alarm ratio and false alarm rate for the two contingency tables shown above by dragging the correct answer to the appropriate boxes in the table.

correct

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Please put the labels on one of the existing boxes.

You have completed the exercise