...
Essentially, it's a reformatting of the FalsePositive percentage and FalseNegative percentage, as 'spam hit rate / ham strike rate'. This can be computed from FP%/FN% as follows:
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let fp = false positive percentage |
...
let fn = false negative percentage |
...
batting average hitrate = (1 - (fn / 100)) |
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batting average strikerate = (fp / 100) |
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batting average = "hitrate/strikerate" |
so if you have an FP% of 0.1%, and an FN% of 2.5%, the batting average is
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(1 - (2.5 / 100)) "/" (0.1 / 100) = |
...
.975/.001 |
See also MeasuringAccuracy for other schemes used, or FpFnPercentages for the main one we use in SpamAssassin.