AQL specified in a standard

The ANSI/AAMI PB70:2012 standard for surgical gowns specifies an AQL of 4%, and defines it "... the quality level that for the purpose of sampling inspection is the limit of a satisfactory process average." Does this imply that gowns from a manufacturing process that produces more than the AQL of 4% defects do not meet the standard?

(obDisclaimer : I'm not representing my employer here)

 

The key phrase here is " ... for the purpose of sampling inspection ... " If your process produces more than 4% defective, the 4.0 AQL sampling plan will accept some lots and reject some lots. Rejected lots will have to be scrapped or sorted/reworked and re-sampled for conformance. Soon, you will be driven into the tightened sampling inspection tables, and the proportion of lots that the plan rejects will increase; sorting/rework costs will increase. Then you will probably choose to implement an improvement to the process to decrease the process average defective so you make it back to the normal sampling table and perhaps to the reduced sampling table.

A better implication, in my opinion, is that when the 4.0 AQL sampling plan and attendant switching rules are followed for acceptance, the result will be a process average to the customer of 4.0% defective or lower. You could have a manufacturing process average of 10% defective, add a sorting/rework operation that is part of the manufacturing process before acceptance sampling and have an end-of-process average defective to the customer far lower than 4.0%, depending on the effectiveness of the sorting/rework operation. However, that would likely cause you to increase prices and lose business to those competitors with a lower manufacturing process average defective and lower costs because they don't have to sort/rework to meet the 4.0 AQL sampling plan.

 

Interesting! I think I understand now- it seems the AQL is used to determine a conforming sampling plan, and lack of a 'satisfactory process average' does not mean it's not a compliant gown. Part of my confusion was due to the standard also specifying a RQL of 20% with 90% confidence. It seems odd to specify the AQL in this type of product standard. With both AQL and RQL specified, it seems like some sampling plans wouldn't meet the standard because they'd be too stringent. If the sampling plan rejects lots with 4% defective more than 5 times out of a hundred, then that ain't an AAMI PB70 compliant gown! In the few quality system classes I've attended, I've been told not to write that I'll hit myself with a hammer- but it seems to be baked into this standard