Low Bucket Observed Fraction - Calibration Bins, Exactly

Count the low bucket observed fraction exactly.

highlighted = computed this step

Count the low bucket positives

Only row E has label 1. Rows F, G, and H have label 0.

1 + 0 + 0 + 0 = 1

The low bucket also has 4 rows.

\text{rows in low bucket}=4

The observed positive fraction is 1 over 4.

\text{observed low}={1\over4}