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Table of Contents

Relative Operating Characteristics (ROC)

The Relative Operating Characteristics give a measure of the effectiveness of a forecast system to predict an event that actually happens balanced against forecast of an event that fails to occur.   ROC is derived from measuring the area beneath the results plotted on a ROC diagram.  ROC area values indicate:

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Fig8.3.3-1: ROC diagram for 850hPa temperature for the verifying period Sep, Oct, Nov derived from seasonal forecast runs with data time of early Aug.  Points above the lower left/upper right diagonal signify skill.  The ROC score or value is the area beneath the red curve.


Reliability diagrams

The Reliability diagrams give a measure of the tendency of the forecast system to over- or under-forecast and event.  The diagram plots the frequency of a forecast probability of an event against the frequency that the event occurs.   Ideally these should match and is shown by the diagonal line. Where the plot lies:

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