Statistical Quality Control and Measurement Uncertainty

The laboratory needs to demonstrate that its own measurements are under control. This is separate from production quality: what is being measured here is not the product, but the laboratory itself .

Scope

• Control charts: Graph of control sample results over time; automatic evaluation of control and warning limits, drift and trend rules.
• Repeatability and reproducibility: Monitoring differences between repetitions of the same analyst and between different analysts and instruments.
• Measurement uncertainty: Calculation and reporting of uncertainty budget components.
• Proficiency tests: Recording of external comparison results, z-score evaluation, and initiating action in case of adverse results.
• Process capability indicators: Monitoring the distribution of product results according to specification; seeing not only whether they are suitable/not suitable, but also how much the margin has narrowed.
• Laboratory performance indicators: turnaround time, repeat analysis rate, out-of-specification rate, instrument downtime, first-attempt correct result rate.