Attribute MSA Study Requirements? Marginally good & marginally bad with good & bad

ozziegood

Registered Visitor
#1
Hello All-
I am wondering what exactly is required for a MSA study for attribute data? We are using a Go/NoGo gage and for the PPAP I need to perform a MSA study. I have read the manual but it is still a bit fuzzy to me. Thanks in advance!
 
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Jim Wynne

Staff member
Admin
#3
ozziegood said:
Hello All-
I am wondering what exactly is required for a MSA study for attribute data? We are using a Go/NoGo gage and for the PPAP I need to perform a MSA study. I have read the manual but it is still a bit fuzzy to me. Thanks in advance!
If you could be more specific as to what's confusing you, we can try to help.
 

Helmut Jilling

Auditor / Consultant
#4
ozziegood said:
Hello All-
I am wondering what exactly is required for a MSA study for attribute data? We are using a Go/NoGo gage and for the PPAP I need to perform a MSA study. I have read the manual but it is still a bit fuzzy to me. Thanks in advance!

A common format is 3 x 3 x 10. Three test people taking 3 readings each of 10 parts. I have also seen 10 x 2 x 2.
 

Jim Wynne

Staff member
Admin
#5
hjilling said:
A common format is 3 x 3 x 10. Three test people taking 3 readings each of 10 parts. I have also seen 10 x 2 x 2.
That's for a variables study, Helmut (a standard GR&R study). The OP is (I assume) referring to Section 3 of the AIAG MSA manual for attributes studies.
 

Helmut Jilling

Auditor / Consultant
#6
Jim Wynne said:
That's for a variables study, Helmut (a standard GR&R study). The OP is (I assume) referring to Section 3 of the AIAG MSA manual for attributes studies.
You're right. ...Maybe I shouldn't reply late at night...
 
C

cyberjyothi

#7
Re: Attribute MSA Study Requirements?

Hello folks,

During our surveillance audit, we face one question from the auditor on how do you perform the attribute study using good,bad,marginally good and marginally bad samples.

can any one help me on how to do attribute study with marginally good & marginally bad along with good& bad.

from my process we are not finding any marginally good/bad samples.The auditor ask us to forcefully make the above samples and perform the study.

I look forward to get the relevent details from u and suggest me how to proceed further.

:thanx:

With regards,
Jyothiswar.M
 

Jim Wynne

Staff member
Admin
#8
Re: Attribute MSA Study Requirements?

cyberjyothi said:
Hello folks,

During our surveillance audit, we face one question from the auditor on how do you perform the attribute study using good,bad,marginally good and marginally bad samples.

can any one help me on how to do attribute study with marginally good & marginally bad along with good& bad.

from my process we are not finding any marginally good/bad samples.The auditor ask us to forcefully make the above samples and perform the study.

I look forward to get the relevent details from u and suggest me how to proceed further.

:thanx:

With regards,
Jyothiswar.M
The important thing about an attributes study is that you demonstrate that the gage (or system) is capable of detecting "bad" parts without also rejecting "good" ones. This means, as your auditor has pointed out, that you need parts near the limits. Is there some reason you can't produce some marginal parts for the study? Sometimes there is good reason, in which case you need to demonstrate that for the purposes of verifying the system, "bad" or marginal parts aren't necessary. You might do this by showing a statistical analysis that demonstrates that the process is well-centered, in control, and producing parts near the limit is highly unlikely. Nevertheless, it seems that if you're using an attributes gage, you are concerned about marginal parts, so you'll need to demonstrate the efficacy of the system, or use variables measurement.
 
H

HRinAZ

#9
You need to perform what is called “Attribute agreement analysis” study. Here are some basic guidelines for conducting an attribute study:

1) Select 10 parts or samples for inspection. These samples should include some clearly good, some clearly bad, and some borderline. Overall, I would try to end up with 5-6 good and 4-5 bad.

2) Have 2 appraisers inspect the samples in random order. They should each do this twice. This will allow you to assess how often they agree with each other (reproducibility) and how consistent they are in their own assessments (repeatability).

3) Compare these results to the standard. This part can be tricky. When you put the study together, you should have a team or expert do this evaluation. I say it is tricky because many times, the standards are just being developed or haven't been developed at all. To perform this study correctly the standard should have been established first, prior to beginning this study!

4) Plug the data into Excel or Minitab (preferred) for the analysis. The reproducibility and repeatability of the test method will be evaluated by calculating:
• Percent of the time an appraiser agreed with own results over two trials
• Percent of time an appraiser agreed with other appraiser’s results over two trials
• Percent of time an appraiser agreed with standard over two trials
• Percent of time an appraiser’s agreed with each other and with standard,

Upon test completion, the following statistical calculations should be performed.

Percent of the time an appraiser agreed with own results over two trials

% Agree self = (Total number of times trial 1 results are equal to trial 2 results)/10 *100

Percent of time an appraiser agreed with other appraiser’s results over two trials

% Agree others = (Total number of times trial 1 results are equal to trial 2 results for appraiser 1 and are equal to appraiser 2 results over both trials)/10 * 100

Percent of time an appraiser agreed with standard over two trials

% Agree Standard = (Total number of times trial 1 results are equal to trial 2 results and equal to standard for each appraiser) / 10 *100

Percent of time an appraiser’s agreed with each other and standard over two trials

% Agree standard/others = (Total number of times appraiser 1 agreed with appraiser 2 over both trials and agreed with standard) /10 * 100

So in a nutshell the acceptance criteria we use are:

Output Acceptance Criteria
% Agree Self ≥ 90%
% Agree Others ≥ 81%
% Agree Standard ≥ 90%
% Agree Standard/Others ≥ 73%

You are looking for an overall assessment agreement of 90% or more to accept your measurement system. This means that 90% of the time your appraisers need to agree with themselves, each other and the standard. Deficiencies should be addressed with training and development of standards (basic rules, visuals, etc).
 
J

jager

#10
Re: Attribute MSA Study Requirements? Marginally good & marginally bad with good & ba

Would this be for the Attribute Gage Study? How about for the attribute study showing we have good parts? I remember one company asking for 300 pieces to be passed through a gage as a flatness attribute study. Their variable dimensions required a Cpk of 1.67 as usual. I was wondering if there is a form where you just check "Pass" 300 times, and "Fail" hopefully zero times. Is there a form like that?
 
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