# Three Methods to Analyze Gage R&R Studies

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Thanks so much for reading our publication. We hope you find it informative and useful. Happy charting and may the data always support your position.

Sincerely,

Dr. Bill McNeese
BPI Consulting, LLC

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• DaleWJuly 2, 2015

From reading Wheeler, my understanding is that the fault here lies with the AIAG (using % of total standard deviation) rather than anything about the Average & Range method of interpretation.Running your Gauge R&R example data in Minitab 17, I found that its two available methods (ANOVA and Average & Range) give practically indentical results, where for both the reported % of variance is useful and the reported % of standard deviation isn't (and adds up to well over 100% for both methods).

• Terrance Cleary [email protected]September 26, 2015

My question is about how to handle a measurement that is a vector.   In my particular case, I am looking at an Unbalance reading of a rotor that has a magnitude and an angle.  I am only looking at Static Balance.  If I visualize the total tolerance zone of a certain magnitude, the tolerance zone would be a 360  degree tolerance zone of radius of what the maximum permissible deviation from the perfect part would be.   Now, if I wanted to find the  If I visualize the tolerance zone, I would see that it is basically a circle.  I would say that the diameter of the circle would be basically the diameter of the circle as described by the range of say 30 measurements of the same part.   Then, I would say that the P/Tol would be the area or the Repeatability/ Area of the total Tolerance Zone.    Do you agree with my assessment.   Is there a program developed for such a meaurement?

• billOctober 19, 2021

Hi Terrance,
I have not done anything with measurements that are a vector and how to handle process capability with that. I am sure that there are programs to handle it.  Try searching for multiple process capability vectors.

• John LOctober 22, 2015

Our manufacturing partner in Asia uses an Excel template for the Average and Range Method.  However, their template does not compute the part variation, nor total variation.  The % variation is done be dividing EV, AV, and R&R by the Tolerance (USL-LSL).  Does anyone endorse this particular statistic?

• billOctober 22, 2015

It depends on what you are using the test for.  If you are using it for control charting and process capability, you want to use the total variation because you want the test to be able to tell the difference between samples from the process.  However, if you are just using the test to see if the product is in or out of spec, you use the tolerance range.  Both are widely used depending on the purpose of the test method.

• AshokAugust 24, 2017

Dear Bill,Kindly share links or example where GRR has been done on two similar machines for destructive sampling. RegardsAshok

• billAugust 25, 2017

Hello Ashok,

• DennisFebruary 21, 2018

Does anyone have the table of the d2* constants ?

• billFebruary 21, 2018

These are available in a number of books (like Dr. Wheeler's).   You call also search online for d2* constants to find some results.

• BenHSeptember 5, 2018

This is a very thorough article, easy to read and understand. I've been manipulating GRR template files without understanding the basics of it and found it confusing recently when I got different results using JMP software.This article helped me greatly understanding. Thank you so much!

• Akhil January 6, 2021

What is the percentage of study variation and repeatability and also NDC target..

• Khennane January 18, 2021

What is the origin of the table of the constant d2 the R&R stady ??

• billJanuary 18, 2021

d2 is a bias correction factors; they come from "Tables of Range and Studentized Range" Annals of Mathematical Statistics, v.31, pp. 1122 – 1147, 1960 by H. L. Harter.  You might check this article out:  https://www.spcpress.com/pdf/DJW353.pdf

• TheDudeFebruary 6, 2021

Bill, I am confused by one of your last paragraphs:” Under the AIAG guideline, a test method is acceptable if the % R&R is 10% of less. It is marginal in the range of 10 to 30%. The % R&R for our example data is about 7%. So, it is First Class Monitor and acceptable under AIAG guidelines. “But the AIAG guideline applies to R&R expressed as % of total variation (i.e., square root of variance). 30% as R&R/TV means 9% as R&R/Total variance. So that would be the threshold for AIAG-marginal. Can you please clarify?

• keyurJuly 6, 2021

if two measuring methods are used how to find who has better repeatability ? The higher value or lower value is considered?

• billJuly 6, 2021

The system  with the lower measurement system standard deviation will be more repeatable.