Process Analysis Gage Repeatability and Reproducibility - Computational Approach
You can think of each measurement as consisting of the following components:
- A component due to the characteristics of the part or item being measured,
- A component due to the reliability of the gage, and
- A component due to the characteristics of the operator (user) of the gage.
The method of measurement (measurement system) is reproducible if different users of the gage come up with identical or very similar measurements. A measurement method is repeatable if repeated measurements of the same part produces identical results. Both of these characteristics - repeatability and reproducibility - will affect the precision of the measurement system.
We can design an experiment to estimate the magnitudes of each component, that is, the repeatability, reproducibility, and the variability between parts, and thus assess the precision of the measurement system. In essence, this procedure amounts to an analysis of variance (ANOVA) on an experimental design that includes as factors different parts, operators, and repeated measurements (trials). We can then estimate the corresponding variance components (the term was first used by Daniels, 1939) to assess the repeatability (variance due to differences across trials), reproducibility (variance due to differences across operators), and variability between parts (variance due to differences across parts). If you are not familiar with the general idea of ANOVA, you may want to refer to ANOVA/MANOVA. In fact, the extensive features provided there can also be used to analyze repeatability and reproducibility studies.