Next-day (1-day lead time) X flare forecast "reliability" during the period 1986 to 2006. The top panel plots the observed relative frequency of X flare days (days on which an X flare occurred) against their corresponding forecasts, grouped in 5% (0.05) bins. The dashed diagonal line represents perfect correspondence. Points falling below the diagonal indicate a tendency of the forecasts within that bin to overpredict the occurrence of X flares while points above the diagonal indicate underprediction. The error bars in the top panel correspond to the standard error associated with the number of forecasts in each bin. The number of forecasts in each bin is plotted in the bottom panel histogram. Note that the histogram Y-axis scale is logarithmic.

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