A yes/no prediction on a NorthPeak machine can be right in two ways and wrong in two ways. A caught fault sends a technician to a real problem. A false alarm costs one visit. A missed fault costs downtime and a repair, about 1,160 CAD on average in incidents.csv. The confusion matrix counts those four cases on the test quarter, and precision, recall and F1 summarise them. F1 is the harmonic mean of precision and recall (a mean that stays low when one of the two numbers is low). This lesson reads the matrix of the Lesson 3 logistic regression cell by cell and shows why accuracy alone hides the real story.
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