Table 2.
Evaluation of precision, accuracy, and z-score between laboratories for CRM.
| Parameter | Lab 1 | Lab 2 | Lab 3 |
|---|---|---|---|
| Mean value, mg/kg | 20.67 | 21.25 | 20.24 |
| Number of sample, n | 3 | 3 | 3 |
| Precision | |||
| Relative standard deviation (% RSD) | 8.63 | 1.20 | 3.39 |
| Accuracy | |||
| Certified reference value, mg/kg | 19.06 ± 0.86 | ||
| Bias, mg/kg | −1.61 | −2.19 | −1.18 |
| Standard deviation (σ)1) | ±1.91 | ||
| (10% RSD), mg/kg | |||
| ±2 σ, mg/kg | ±3.81 | ||
| z-score2) | 0.84 | 1.2 | 0.62 |
1)19.06 mg/kg as 10% RSD.
2)Z = (xlab − Xref)/σ, where Z is z-score; xlab is participant result; Xref is certified reference value; σ os standard deviation.
|z| ≤ 2 is satisfactory.
2 < |z| < 3 is questionable.
|z| ≥ 3 is unsatisfactory.