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📊 Proficiency Testing Z-score (PT)
CNAS inter-laboratory comparison: Z=(x−median)/s, |Z|≤2 satisfactory
Reported values of each lab (one per line or space-separated)
Decision logic (Proficiency testing / robust statistics, CNAS-GL002)
· Z = (x − assigned/median value) / s; s can be the scheme-specified standard deviation, or estimated from this batch (ordinary SD or robust MAD×1.4826).
· Decision: |Z|≤2 satisfactory; 2<|Z|≤3 questionable (needs review); |Z|>3 unsatisfactory (problem present).
· Mostly used for inter-laboratory comparison; this tool also works for evaluating a single result against a reference value.
About PT Z-Score (Proficiency Testing)
Proficiency testing Z-score calculator per ISO 13528: |Z|<=2 satisfactory, 2-3 questionable, >=3 unsatisfactory, with robust statistics.
Learn more about this tool →
Lab QC & Levey-Jennings
Analytical Method Validation
Calibration Curve & Linearity
Method Comparison (Bland-Altman)
GUM Measurement Uncertainty
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