Deviating from AQL in a small Retail Apparel Company

P

Perfectol

#1
I am the QA manager for a small retail apparel company and everything that I'm learning is self taught OJT (which is not much at all) and need assistance calculating the following:

AQL
AOQ
AOQL
PROCESS AVERAGE
operating characteristic
Probability of accepting a lot

Manufacturing is farmed out. We don't build anything in house.
Inspection is only performed after the product is made and delivered to us. There is no inspection of components or du-pro inspection at this time.

We receive anywhere from 300 to 2000 units of any one style. Most of the time it is in the 500-600 units.

Based on a 500 unit delivery and a normal inspection level, we are to inspect 50 units. Sometimes, due to one reason or another out of my control, we only have time to inspect a portion of that amount. Do the formulas take into account this variable or must every unit be inspected (50 units)?

We have a visual pass/fail inspection and a measurement portion.
 
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Statistical Steven

Statistician
Staff member
Super Moderator
#3
I am the QA manager for a small retail apparel company and everything that I'm learning is self taught OJT (which is not much at all) and need assistance calculating the following:

AQL
AOQ
AOQL
PROCESS AVERAGE
operating characteristic
Probability of accepting a lot

Manufacturing is farmed out. We don't build anything in house.
Inspection is only performed after the product is made and delivered to us. There is no inspection of components or du-pro inspection at this time.

We receive anywhere from 300 to 2000 units of any one style. Most of the time it is in the 500-600 units.

Based on a 500 unit delivery and a normal inspection level, we are to inspect 50 units. Sometimes, due to one reason or another out of my control, we only have time to inspect a portion of that amount. Do the formulas take into account this variable or must every unit be inspected (50 units)?

We have a visual pass/fail inspection and a measurement portion.
You can calculate the AQL and LQ (LTPD) for any sample size with any number of acceptable defectives in the sample. If you are suppose to sample 50, but instead curtail the inspection once started, you can calculate the AQL, but keep in mind you have a bias in your sampling.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
Steve - it might be helpful to provide those formulas since the OP is a 'newbie' to acceptance sampling. (finding them in jungle will be tough and deriving them even tougher for someoen as new as he is)

Perhaps just the set with a c=0 number? that is most likely to be what the OP's organization does...
 

Statistical Steven

Statistician
Staff member
Super Moderator
#5
Steve - it might be helpful to provide those formulas since the OP is a 'newbie' to acceptance sampling. (finding them in jungle will be tough and deriving them even tougher for someoen as new as he is)

Perhaps just the set with a c=0 number? that is most likely to be what the OP's organization does...
Here is an example of the calculations
 

Attachments

J

JoeDM

#6
If you're new to this stuff, I would suggest you use a standard sampling plan like MIL-STD-105, but consider two stage sampling. This avoids the mathematics, but can significantly reduce inspection.

The theory goes that product is either very good or very bad. If it is very good, you will accept the lot on the first sample (which is smaller that the sample size for a single sampling plan). If the product is very bad, you'll reject on the first sample. If you guessed wrong and the product quality is somewhere in between, then a second sample is required, and you end up doing more inspection than you would have with single sampling.

I used this technique with great success and rarely needed to go to a second sample. Using this technique, I took a department that never seemed to be able to inspect on time and turned it into one that was always on time.

Good luck! Hope this helps.
 
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