Calculation of a Health Index of Oil-Paper Transformers Insulation with Binary Logistic Regression

Table 3

Classification table with six factors.

Actual group	Predicted		Actual group size	Percentage correctly classified
	0	1
0 (health)	19	2	21	90.5%
1 (unhealthy)	0	9	9	100%
Predicted group size	19	11	30	93.3%

The number of transformers correctly assigned to group 0 (healthy) is 19, whereas 2 transformers of group 0 (healthy) are incorrectly assigned to group 1 (unhealthy). Similarly, the number of correct classifications to group 1 (unhealthy) is 9, and the number of incorrect assignments to group 1 (unhealthy) is 0.
Percentage correctly classified = (number correctly classified/total number of observations) × 100%.
For example, 90.5% = (19/21) × 100%; 93.3% = (19 + 9)/30  ×  100%.