Introduction
Evaluating a classifier is often trickier than evaluating a regression model. With regression, an error of 5,000. With classification, not all mistakes are equal:
- A spam filter that sends an important job offer to the spam folder (false alarm) is annoying.
- A cancer screening test that tells a sick patient "you're fine" (missed case) can be deadly.
A single number like accuracy treats these the same. This chapter gives you better tools, starting with the most important one: the confusion matrix.