Measurement system analysis (day 15)

We introduced the concept of bias in the previous section. Measurement system analysis (MSA) enables you to identify the specific biases that are caused by the system of measurement itself. Total process variation typically comprises variations from two sources— variation inherent in the process and variation due to measurement. Mathematically, this may be represented as:

σ ² total = σ ² process + σ ² measurement

The measurement system needs to be analyzed for the following:

Parameter	Definition
Accuracy	Difference in the average measurement compared to a standard
Repeatability	Variation in measurements when the same person repeats the measurement with the same measuring equipment
Reproducibility	Variation in measurement when two or more people take measurements with the same measuring equipment
Stability	Variation in the measurement over an extended period of time when measurements are done by the same person with the same equipment
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