Gage Repeatability & Reproducibility Results - Quick Tab

Click the Range method variance estimate button to display a spreadsheet containing the estimates for the variance components (Sigma and Sigma squared), that is, for the repeatability (error due to differences between trials), reproducibility (error due to differences between operators or appraisers), combined repeatability and reproducibility, and part-to-part variability. For computational details refer to the Technical Notes.

Click the Range method percent tolerance button to display a Percent Tolerance Analysis spreadsheet, which is computed using the settings of the options on the Gage Repeatability & Reproducibility Results dialog box -

Options

tab, where you specify the tolerance value for parts and the number of Sigma intervals. The computational formulas for most of these computations are described in the Technical Notes. In short, the tolerance value will be used to compute the percent tolerance values, that is, to express the variability due to reproducibility and repeatability errors relative to the engineering tolerance. The number of Sigma intervals parameter will be used to determine the range of repeatability and reproducibility errors; by default (number of Sigma intervals = 5.15), this range contains 99% of the errors, assuming the normal distribution. The Percent Tolerance Analysis spreadsheet contains variability estimates and percentage values; (for an example, see ASQC/AIAG, 1990, pages 71,72).

In the spreadsheet, the first column contains the estimates of Sigma (for repeatability, reproducibility, etc.) times the number of Sigma intervals. The second column contains the percentage values (for the ranges in the first column) relative to the total (study) variation range; the third column contains the percentage values relative to the total variance (% Total Contribution), and the fourth column contains the percentage values relative to the tolerance values. If the percent of total variation range or tolerance for repeatability and/or reproducibility is less than 10%, the gage system is usually considered acceptable; percentage values between 10% and 30% may be acceptable based upon the importance of the respective application, cost of gage, cost of repairs, etc. (see ASQC/AIAG, 1991, page 127).

Note: Experiments with single trials. If the current R & R study includes only a single trial for each operator and part (i.e., it is a short study), then some of the variance components cannot be estimated. Specifically, the repeatability and reproducibility components cannot be estimated separately, and only the combined R & R component will be reported.

Click the Repeatability & reproducibility plot button to produce the standard plot to summarize the results of a repeatability and reproducibility study with multiple trials. This plot is discussed in detail in the Introductory Overview. To review, each point in this plot represents the deviation of the respective measurement from the average rating of the respective part (across trials and operators). Multiple trials (measurements) are connected by a vertical line. The dashed line within each box represents the average deviation of the respective operator from the average ratings by all operators. Thus, this plot allows us to simultaneously visualize the bias of each operator when rating the parts, the variability within each operator (height of the box), as well as the variability across trials for each part and operator (the length of the vertical lines). Put another way, if there is perfect reproducibility, the dashed lines for all operators will be at exactly the same level (at zero). If there is perfect repeatability, all repeated trials will yield identical results; thus all vertical lines will be of "zero height," that is, only points will be visible in the plot.

ANOVA method variance estimate. The ANOVA method variance estimate button is only available if the current experiment contains more than one trial. Click the ANOVA method variance estimate button to display a spreadsheet with the estimates for the variance components (Sigma and Sigma squared), that is, for the repeatability (error due to differences between trials), reproducibility (error due to differences between operators or appraisers), combined repeatability and reproducibility, and part-to-part variability. If the No 2-way interaction check box is not selected on the Gage Repeatability & Reproducibility Results - Advanced tab, a separate variance estimate will be computed for the operator by part interaction component. For all Sigma estimates, the lower and upper confidence limits (according to the Proportion for confidence interval value) will also be reported. For computational details refer to the Technical Notes.

The ANOVA method is only available if the current experiment contains more than one trial. Click the ANOVA method percent tolerance button to create a Variance Components spreadsheet, which is computed using the settings of the options on the Gage Repeatability & Reproducibility Results dialog box -

Options

tab, where you specify the tolerance value for parts and the number of Sigma intervals. In the spreadsheet, the first column contains the estimates of Sigma (for repeatability, reproducibility, etc.) times the number of Sigma intervals; the second and third column contains estimates of the lower and upper confidence limits for these ranges. The fourth column contains the percentage values (for the ranges in the first column) relative to the total (study) variation range; the fifth column contains the percentage values relative to the total variance (% Total Contribution), and the sixth column contains the percentage values relative to the tolerance values. If the percent of total variation range or tolerance for repeatability and/or reproducibility is less than 10%, the gage system is usually considered acceptable; percentage values between 10% and 30% may be acceptable based upon the importance of the respective application, cost of gage, cost of repairs, etc. (see ASQC/AIAG, 1991, page 127).