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98
CHAPTER 9. CLASSIFICATION
Figure 9.3: Our example ROC
Example 9.1. Suppose you have a test set of 10 cases, whose actual class
you know, and you classifier outputs the following numbers. The cases are
listed below in descending order.
case
1
2
3
4
5
6
7
8
9
10
Class(case)
.97
.93
.87
.70
.65
.58
.43
.33
.21
.05
actual
True
True
False
False
True
False
True
False
True
False
With the first threshold, − inf, you classify no cases as true and, hence, have
no true or false positives, i.e. the first point on ROC is (0, 0). With the