z-score (proficiency testing)
Definition
A performance statistic in PT defined as z = (x - X) / s_PT, where x is the laboratory's result, X is the assigned value, and s_PT is the standard deviation for proficiency assessment. |z| ≤ 2 is satisfactory, 2 < |z| < 3 is a warning, and |z| ≥ 3 is unsatisfactory under ISO 13528.
Related terms
- Combined standard uncertainty
- The overall standard uncertainty of a result, obtained by combining all Type A and Type B component uncertainties in quadrature (square root...
- Expanded uncertainty
- The combined standard uncertainty multiplied by a coverage factor k, chosen to achieve a stated coverage probability. For a normal distribution, k...
- GUM
- Guide to the Expression of Uncertainty in Measurement. The international standard, maintained by eight metrology and standardisation bodies, that defines Type A...
- Type A uncertainty
- Uncertainty evaluated by statistical analysis of a series of observations. The standard uncertainty is the standard deviation of the mean (standard error)...
- Type B uncertainty
- Uncertainty evaluated by means other than statistical analysis of repeated measurements. Sources include calibration certificates, instrument specifications, reference data, and expert scientific...
Explained in
- Measurement Uncertainty and Proficiency TestingA performance statistic in PT defined as z = (x - X) / s_PT, where x is the laboratory's result, X is the assigned value, and s_PT is the standard deviation fo...