PPM - Filtering Defects out of calculation

QualityMoo

Starting to get Involved
#1
I am interested in thoughts/opinions/best practice when calculating PPM and filtering out defects from the calculation.

Situation: We calculate Supplier PPM each month based on quantity of parts written up on nonconformance reports during the month against quantity of part reciepts for the month. Period.

I have been asked to remove all the defects where the disposition of the nonconformance was "Use As Is".

In my opinion these should still be part of the PPM calculation. Regardless of the disposition, we had nonconforming product.

Thoughts or comments please.
 
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QualityMoo

Starting to get Involved
#3
Thank you Golfman25. I did a quick check and it did make a noticable difference. Although, the trend line did not change that much.

I think that this is an issue more of principles.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
it is a matter of principle - or ethics or trying to stop your managemetn from deluding itself.

I understand the desire to remove 'use as is' defects. why 'punish' anyone for an event that was truly "no harm, no foul"?

the key here is that the ppm calaculation isn't about punishment or score keeping; its about identifying opportunities for improvement. (it also satisfies the requirement to assess your suppliers if you are registered to one or more of the common QMS standards).

guide your management to see that the supplier did in fact send you non-conforming parts per your specifications, the fact that the specification is too tight is not for the supplier to judge. good suppliers meet the specification; how will they feel if the next time the supplier sends non-conforming parts (they 'got away with it' once...) they are completely unusable or worse, they escape to your customer and become a complaint against you?

Guide your management to understanfing that the appropriate response is to change the specification, not ignore it...
 

Statistical Steven

Statistician
Staff member
Super Moderator
#5
I am interested in thoughts/opinions/best practice when calculating PPM and filtering out defects from the calculation.

Situation: We calculate Supplier PPM each month based on quantity of parts written up on nonconformance reports during the month against quantity of part reciepts for the month. Period.

I have been asked to remove all the defects where the disposition of the nonconformance was "Use As Is".

In my opinion these should still be part of the PPM calculation. Regardless of the disposition, we had nonconforming product.

Thoughts or comments please.
Just change the metric to PPM out of specification regardless of the disposition. I think Bev hit the nail in the head. You calculate metrics to guide management to make decisions such as changing specifications or changing vendors.
 

Golfman25

Trusted Information Resource
#6
While it is all well and good, if the disposition is "use as is" is it really a "defect." You would have a hard time convincing me to spend a lot of time and resources to correct it when there are real defects causing real problems which merit attention. So I would use two numbers -- adjusted and unadjusted PPM. It might give you a picture of how many non-substantial "defects" you're dealing with.

And in many cases, you'll need an act of Congress to change a specification. :)
 
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