ANOVA Analysis - Trying to understand MSA analysis- Please review my spreadsheet

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Statistical Steven

Statistician
Staff member
Super Moderator
#12
No. A Linearity study may be used to verify the gage over the entire range of measurement.
Why not use parts across the entire range? Just put part into the ANOVA model to eliminate part to part variaiblity (this will be highly significant) then you can get a pooled estimate across the range. If you do a linearity study you assume constant variance across the range (assuming you use regression analysis), so why not get a pooled estimate across the entire range?
 
P

prabhudvp

#13
Hi

For Attribute Gage R&R what is the Sample size
The TS auditors likes to measure 100 parts
but i could not find the this number in the MSA manual

Regards

D.Prabhu
 

Stijloor

Staff member
Super Moderator
#14
Hi

For Attribute Gage R&R what is the Sample size
The TS auditors likes to measure 100 parts
but i could not find the this number in the MSA manual

Regards

D.Prabhu
Hello Prabhudvp,

Can you clarify why the TS Auditors "required" 100 parts for an attribute gage study? Was there a Customer-specific requirement? If not, you could ask the auditor: "where is the requirement that states that we must use 100 parts?"

I am curious about the reponses from MSA Specialists here at The Cove.

Stijloor.
 

Miner

Forum Moderator
Staff member
Admin
#15
Why not use parts across the entire range? Just put part into the ANOVA model to eliminate part to part variaiblity (this will be highly significant) then you can get a pooled estimate across the range. If you do a linearity study you assume constant variance across the range (assuming you use regression analysis), so why not get a pooled estimate across the entire range?
You can get away with this if your study aim is soley for this purpose, or to obtain the P/T Ratio. If you want the %GRR, your samples MUST reflect the actual process variation. Otherwise, you invalidate the results of the study.
 

Miner

Forum Moderator
Staff member
Admin
#16
When looking at the %GRR numbers, what is the breaking point between acceptable and unacceptable. Below is some data from a study we did.

Variation | St Dev | %TV | %Cont
Eq Variance (EV) 3.681E-08 | 1.151E-03 | 0.47% | 37.06%
Interaction (INT) 2.152E-08 | 1.291E-07 | 0.00% | 21.67%
Appraiser (AV) 2.103E-08 | 8.701E-04 | 0.35% | 21.17%
System (GRR) 7.936E-08 | 1.443E-03 | 0.59% | 79.90%
Part (PV) 1.996E-08 | 8.478E-04 | 0.34% | 20.10%
Total Variation 9.933E-08 | 2.465E-01 | 100.00%

Thanks
Typically, < 10% is excellent, 10 - 20% is acceptable, 20 - 30% is okay if the dimension is non-critical and the expense of improving the gage is not warranted, and > 30% is not acceptable. Also, there is more detail in other posts within this forum.
 
O

OceanDiver

#17
Typically, < 10% is excellent, 10 - 20% is acceptable, 20 - 30% is okay if the dimension is non-critical and the expense of improving the gage is not warranted, and > 30% is not acceptable. Also, there is more detail in other posts within this forum.
Variation | St Dev | %TV | %Cont
Eq Variance (EV) 3.681E-08 | 1.151E-03 | 0.47% | 37.06%
Interaction (INT) 2.152E-08 | 1.291E-07 | 0.00% | 21.67%
Appraiser (AV) 2.103E-08 | 8.701E-04 | 0.35% | 21.17%
System (GRR) 7.936E-08 | 1.443E-03 | 0.59% | 79.90%
Part (PV) 1.996E-08 | 8.478E-04 | 0.34% | 20.10%
Total Variation 9.933E-08 | 2.465E-01 | 100.00%

So looking at this data you say that the GRR should be < 30%. Is the % Total Variation number or the % Contribution number the one to look at? The %TV is 0.59%, extremely low while the % Contribution is 79.90% completely unacceptable.
If neither of these values are the correct one then what do you look at?

Thanks
 

Miner

Forum Moderator
Staff member
Admin
#18
Variation | St Dev | %TV | %Cont
Eq Variance (EV) 3.681E-08 | 1.151E-03 | 0.47% | 37.06%
Interaction (INT) 2.152E-08 | 1.291E-07 | 0.00% | 21.67%
Appraiser (AV) 2.103E-08 | 8.701E-04 | 0.35% | 21.17%
System (GRR) 7.936E-08 | 1.443E-03 | 0.59% | 79.90%
Part (PV) 1.996E-08 | 8.478E-04 | 0.34% | 20.10%
Total Variation 9.933E-08 | 2.465E-01 | 100.00%

So looking at this data you say that the GRR should be < 30%. Is the % Total Variation number or the % Contribution number the one to look at? The %TV is 0.59%, extremely low while the % Contribution is 79.90% completely unacceptable.
If neither of these values are the correct one then what do you look at?

Thanks
Please attach your raw data. Your %TV numbers do not "look right" to me.

%GRR should be assessed against the %TV or % Study Var (Minitab). The %Cont just provides a quick Pareto analysis of the sources of variation.
 
O

OceanDiver

#19
Please attach your raw data. Your %TV numbers do not "look right" to me.

%GRR should be assessed against the %TV or % Study Var (Minitab). The %Cont just provides a quick Pareto analysis of the sources of variation.
I did find an error in my calculations which I did fix. The numbers look "more real" now. But I still do not if this would be good or not.
The raw data is in the "Calc1" worksheet. Thanks
 

Attachments

Miner

Forum Moderator
Staff member
Admin
#20
Now it looks right! I see that your decimal points were off by 2 in the results.

This gage is unacceptable. Your results are off somewhat from Minitab. I attached the Minitab Analysis for your review.

Your %GRR results of %Total Variation = 86.22% (Minitab's %SV = 89.39%) is much greater than the 30% max acceptable, so this gage is not acceptable for use in process control provided that the variation of the parts accurately reflects the actual process variation. An ndc = 1 is also unacceptable. Since the P/T Ratio is also unacceptable at 56%, you have a problem with the gage.

The % Contribution shows that the sources of measurement variation are large in all categories (Repeatability, Reproducibility and Operator x Part Interaction). Are your parts subject to variation in form (shape)?
 

Attachments

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