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F-score (F-measure, F1 measure)

An F-score is the harmonic mean of a system’s precision and recall values. It can be calculated by the following formula: 2 x [(Precision x Recall) / (Precision + Recall)]. Criticism around the use of F-score values to determine the quality of a predictive system is based on the fact that a moderately high F-score can be the result of an imbalance between precision and recall and, therefore, not tell the whole story. On the other hand, systems at a high level of accuracy struggle to improve precision or recall without negatively impacting the other. 

Critical (risk) applications that value information retrieval more than accuracy (i.e., producing a large number of false positives but virtually guaranteeing that all the true positives are found) can adopt a different scoring system called F2 measure, where recall is weighed more heavily. The opposite (precision is weighed more heavily) is achieved by using the F0.5 measure.

Read this article on our Community to learn more about F-score.