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Different % Gaugae R&R results in Variability Gauge report

In a Variability Gauge report there are two different %Gauge R&R results cfr. below

 

Why is result 41,1% in Summary Gauge R&R statistics different from Variance Components result = 16,89% ? Which result must be used to report %Gauge R&R?

 

Quality and Process EngineeringRe: Different % Gaugae R&R results in Variability Gauge report

Those are different, because they are different things. First one is calculated using Gauge R&R and Total Variation and other contains variance components. What are you supposed to report? There are many things which could be reported from Gage R&R report, it could for example be % of Tolerance (for Gauge R&R)

Re: Different % Gaugae R&R results in Variability Gauge report

Yes, I see your confusion. The top output is the ratio of standard deviations, which is pretty classic if you do any internet searches of the Gauge R&R literature (e.g., Gauge R&R < 10% is good). But the issue with standard deviations is they are not additive, whereas the variances (standard deviation ^ 2) is. So, it's the classic a^2 + b^2 = c^2, but a + b /= c.

 

The bottom report is looking at variance components, where the total variance would be 62.07887 + 305.42440 = 367.5033. You have 62.07887 / 367.5033 = 16.89%. The top is just going to be the square root of that, so 41.1%.

 

The JMP help menu has good documentation as well Gauge R&R Report.

 

Re: Different % Gaugae R&R results in Variability Gauge report

OK jszarka, thanks, the calculation by variance components is not what is generally used in quality so it is confusing. Would be better to give two different names to both calculations: Gauge R&R is computed using standard deviations but on the other hand indeed the calculation by variance components is statistically correct.