Valueplus 2000 Basic Edition ((TOP))
Note the similarity between the calculation of the SDI and the z-score. They're basically the same thing, but the z-score tends to be used in internal QC programs to compare an individual QC result with the expected values for that material, whereas the SDI tends to be used in external QC programs to compare the performance of the lab with the overall mean for a defined comparative group or with an established target value.
Valueplus 2000 Basic Edition