Evaluation of thyroid hormone synthesis inhibition by reference chemical—sodium perchlorate. A, Population-level concentration-response modeling of the total (N = 32) versus qualified (N = 24) donor cohort. The values were normalized by donor and plotted in aggregate for data modeling. The red band represents the 95% confidence interval of the model fit. The gray band indicates the 95% prediction interval where 95% of future donors would be expected to exhibit bioactivity. B, The model goodness of fit (circles) is represented by the regression coefficient of determination (R²) for the donor population sub-groups (N = 1–32) containing qualified only (blue) or qualified and non-qualified (red) donors. The T4 concentration (triangles) represent the mean T4 production for each donor sub-group. The vertical dashed line indicates the donor acceptance threshold. C, The variability in the IC₁₀ potency (log₁₀ M) point of departure (POD) (circles) is represented for the donor population subgroups (N = 1–32) containing qualified only (blue) or qualified and nonqualified (red) donors. The median (circles) and 95% confidence interval range (error bars) are shown. The T4 concentration (triangles) represents the mean T4 production for each donor subgroup. The vertical dashed line indicates the donor acceptance threshold.