Other common measures of model performance, particularly in Information Retrieval, are Precision and Recall . Precision, defined as P = T P/(T P + FP), is a
measure of how many errors we make in classifying samples as being of class A.
On the other hand, recall, R = T P/(T P + FN), measures how good we are in not
leaving out samples that should have been classified as belonging to the class. Note
that these two measures are misleading when used in isolation in most cases. We
could build a classifier of perfect precision by not classifying any sample as being
of class A (therefore obtaining 0 TP but also 0 FP). Conversely, we could build a
classifier of perfect recall by classifying all samples as belonging to class A. As a
matter of fact, there is a measure, called the F1-measure that combines both
Precision and Recall into a single measure as: F1 = R2+RPP = 2TP+2FNP+FP