Table 5.

Causes of assay invalidity in Vi-PLL ELISA.

Invalidity reason	Number of invalid cases
Non-parallel (slope ratio < 0.80)	26a
Non-parallel (slope ratio > 1.25)	7
10/126 low (<72.7 IU mL−1)	2
10/126 high (>163.5 IU mL−1)	4
10/126 non-parallel (slope ratio < 0.80)	0
10/126 non-parallel (slope ratio > 1.25)	0
Sample H low (<66.7 IU mL−1)	0
Sample H high (>150 IU mL−1)	4
H non-parallel (slope ratio < 0.80)	1
H non-parallel (slope ratio > 1.25)	2
No convergence (cannot fit model)	4
Poor plate precision (wide CI)	3
Total of invalid cases	53 (out of 474b)

^a21 out of 26 cases are for sample K in the Vi-PLL-ELISA by labs 2, 3, 5 and 7.

^bMaximum number of potency estimates possible in this study.