Scores and Boundaries

Move the Threshold

Moving a stated threshold changes class labels by exact comparison. This lesson shows the same score list under two thresholds and recomputes the resulting class counts.

highlighted = computed this step

Start with displayed scores

Use the exact score list -2, -1, 1, and 3. The policy is score at least threshold gives class 1; otherwise class 0.

scores=(−2,−1,1,3)\text{scores}=(-2,-1,1,3)
Move the ThresholdExact score labels and counts are recomputed for each stated threshold.threshold move on exact scoresscores: -2, -1, 1, 3score ≥ threshold gives class 1thresholdclass labelsclass 0 countclass 1 count00 0 1 12220 0 0 131

Compare two thresholds

At threshold 0, the class labels are 0, 0, 1, 1. At threshold 2, the labels are 0, 0, 0, 1.

t=0:0 0 1 1,t=2:0 0 0 1t=0:0\,0\,1\,1,\quad t=2:0\,0\,0\,1
Move the ThresholdExact score labels and counts are recomputed for each stated threshold.threshold move on exact scoresscores: -2, -1, 1, 3score ≥ threshold gives class 1thresholdclass labelsclass 0 countclass 1 count00 0 1 12220 0 0 131

Counts change too

With threshold 0, the counts are class 0: 2 and class 1: 2. With threshold 2, the counts are class 0: 3 and class 1: 1. This is threshold bookkeeping on the displayed scores only.

t=0:(2,2),t=2:(3,1)t=0:(2,2),\quad t=2:(3,1)
Move the ThresholdExact score labels and counts are recomputed for each stated threshold.threshold move on exact scoresscores: -2, -1, 1, 3score ≥ threshold gives class 1thresholdclass labelsclass 0 countclass 1 count00 0 1 12220 0 0 131