Precision and Recall
The traditional method of MeasuringAccuracy in the information-retrieval field is using a two-figure scheme of Precision and Recall.
Given the usual set of 4 numbers (see FpFnPercentages):
Precision and Recall can be computed as follows:
Again, Precision and Recall are part of the standard SpamAssassin statistics data reported in every release. The 'STATISTICS.txt' files distributed with SpamAssassin versions since about 2.30 include this data, measuring the ruleset's accuracy against a validation ruleset:
See also MeasuringAccuracy for other methods.