A few months ago, I wrote an explanation about the “AQL“: what it is and how to use it. I also listed a few frequent questions, but it seems like I forgot one of them:
What AQL tolerance is suitable to my products?
Unfortunately, it is hard to base this on statistical reasoning. So I don’t have any definitive answer.
The right AQL depends on two things, I think:
- The market you are selling into,
- The kind of risk the users run by using/consuming/getting close to your product.
1. The market
The most common AQL chosen by importers is 2.5% for major defects, 4.0 for minor defects, and 0.1 for critical defects. It is considered the “standard” tolerance for most consumer products sold in supermarkets in North America and in Europe.
Based on this standard, you can adjust an AQL that is a bit stricter (say, 1.0/2.5/0.10) if you sell your products in a high-end boutique channel. Or a bit looser (say, 4.0/6.5/0.1) for sale on a low-end market.
2. The user risk
For many car and plane parts, and for pharmaceuticals, the accepted defect rate is much lower than 1%. That’s because bad part might cause death. Specialists often use six sigma tools to reduce the opportunities for defects in every process along the manufacturing cycle.
I am not very familiar with these industries. I guess there are rules of thumb specific to each field.
To sum up:
There are no guidelines for deciding what AQL limits to choose. You have to decide what your tolerance. If the whole batch should not contain more than 1.0% of a certain kind of defect (over the long run), then the AQL should be 1.0% for this kind of defect.
Is it clear?