Z-Primes (PC x NC)

The Z-Prime factor is a commonly used statistical parameter that describes the quality of an assay or a screening plate. It takes into account the separation and the variabilities of two controls (e.g. positive and negative control wells) and ranges from minus infinity to 1.

For groups of data (e.g. wells of plates) Z-Prime factors are calculated for two selected subsets (e.g. positive and negative control wells of a plate). Multiple positive and negative controls can be selected as subsets and the Z-Prime factors will be calculated for all combinations of these. For each group mean and standard deviation (or median and mad) are calculated for the selected subsets.

Z' = 1 - 3 * (sd(x[subset{positive}]) + sd(x[subset{negative}])) / |mean(x[subset{positive}]) - mean(x[subset{negative}])|
or
Z' = 1 - 3 * (mad(x[subset{positive}]) + mad(x[subset{negative}])) / |median(x[subset{positive}]) - median(x[subset{negative}])|

Literature: Zhang, J. et al., J Biomol Screen 1999; 4; 67
Wikipedia: Z-factor