Table 1. Overview of statistical measures for evaluation of HTS assays.

σ = standard deviation; μ = mean; m = median; pos = data set of positive controls; neg = data set of negative controls; n = sample size; F_k = cumulative density function for data set k; max_j = maximum distance between two distributions; SSMD = Strictly standardized mean difference; x_i = ith value of the (ordered) data set x.

Measures	Definition
Kolmogorov-Smirnov-test (KS-test)	KS = maxj(F1(xj) − F2(xj))
t-statistic	$t=\frac{{\mu }_{\text{pos}}-{\mu }_{\text{neg}}}{\sqrt{\frac{{\sigma }_{\text{pos}}^2}{n_{\text{pos}}}-\frac{{\sigma }_{\text{neg}}^2}{n_{\text{neg}}}}}$
Z’-factor	$Z=1-3\frac{{\sigma }_{\text{pos}}-{\sigma }_{\text{neg}}}{{\mu }_{\text{pos}}-{\mu }_{\text{neg}}}$
SSMDMM (method of moment)	${\beta }_{\text{MM}}=\frac{{\mu }_{\text{pos}}-{\mu }_{\text{neg}}}{\sqrt{{\sigma }_{\text{pos}}^2-{\sigma }_{\text{neg}}^2}}$
SSMDML (maximum likelihood)	${\beta }_{\text{MLE}}=\frac{{\mu }_{\text{pos}}-{\mu }_{\text{neg}}}{\sqrt{{\sigma }_{\text{pos}}^2\frac{n_{\text{pos}}-1}{n_{\text{pos}}}+{\sigma }_{\text{neg}}^2\frac{n_{\text{neg}}-1}{n_{\text{neg}}}}}$
SSMDR (robust)	MAD = 1.4826m(|xi − m|)
	${\beta }_{\mathrm{R}}=\frac{m_{\text{pos}}-m_{\text{neg}}}{\sqrt{MA{D}_{\text{pos}}^2-MA{D}_{\text{neg}}^2}}$