How to choose an AQL limit?

by Renaud Anjoran on 10 August 2012

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?

  • A KINGH

    great guy thanks

  • Eric

    Apparently the AQL is readily applicable to products that can be counted as “pieces” and “units”…How can it be applicable to products which are in (liquid) bulk and which are measured in terms of “metric tons”? Pls. help.

  • http://www.qualityinspection.org/ Renaud Anjoran

    Forget about this AQL in this case. Single stage sampling plans by attributes probably don’t make sense. You should probably go for a “accept on zero” plan: either what you test is good, or it’s all rejected.

  • zhen pan

    Renaud,thank you , i have find this for days ,But would you like to give me some suggestion where i can find out the most common AQL for pharmaceuticals.the websites ,forums ,bbs and so on,thanks!

  • http://www.qualityinspection.org/ Renaud Anjoran

    I guess the pharma industry, like the car industry, has such a high quality standard that it doesn’t use the AQL.

  • silvio ciociano

    Hi Renaud, thank you for your website..

    My question is about pharma market, but i’ve to validate only a data migration of critical records..
    should i use AQL? which value?

  • http://www.qualityinspection.org/ Renaud Anjoran

    I don’t know anything about the parma industry, sorry.

  • silvio ciociano

    and about data migration in any industry?
    tks

  • http://www.qualityinspection.org/ Renaud Anjoran

    Please give more information about what you need to do. Why are you trying to use the statistics related to AQL, when it comes to migrating data?

  • silvio ciociano

    Someone tell me to follow the procedure in ISO_2859-4;2002(E) wich contains AQL.
    I’ve to validate a migration from Oracle to SAP with attribute

  • http://www.qualityinspection.org/ Renaud Anjoran

    Oh I see. Iso 2859-4 is totally different from ISO 2859-1 (the standard I describe on this website). i have never worked on ISO 2859-4, so I can’t help. It seems to follow an approach totally different from that of -1.

    For more info, all I can point you to is http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=36164.

  • silvio ciociano

    Thank you very much Renaud

  • Chris

    With my company’s manufacturing for Boeing, for instance, we utilize a C=0 sampling method. I suspect pharmaceuticals use a similar method.

  • http://www.qualityinspection.org/ Renaud Anjoran

    Yes that wouldn’t be surprising.

  • Xuan

    Hi, Anjoran,
    With AQL 2.5, How to change it to percent? Is it the same

  • http://www.qualityinspection.org/ Renaud Anjoran

    Do NOT convert it to percentages. See below for explanation.

    Q: Based on my AQL, I calculated the proportion of defects authorized. Why don’t they correspond to the maximum number of defects authorized?
    A: It is true. In our example above, 2.5% of 200 samples is 5 samples, but we accept the goods even if 10 samples are found with a major defect.
    Why this difference? There are heavy statistics behind this issue. To keep it simple, the producer’s risk is his risk of rejection (based on the random element when drawing the sample) even though his products (if they were all checked) would be accepted. That risk is about 5% in this standard. And, in the same logic, there is a consumer’s risk and is is around 10%. As you can see, this standard is favorable to the producer’s side.

    If you have access to Youtube, you should also watch this video: http://www.youtube.com/watch?v=8bUe8nQpI0s

  • Xuan

    hi Mr Anjoran.

    From http://www.ask.com/question/what-is-aql-2-5 has explaint about AQL 2.5 like this:

    AQL stands for Acceptable Quantity Limit and can be defined as the quality level that is tolerable for consumer goods. AQL 2.5 is a type of limit for most consumer goods which means that 2.5% of the defective goods or products would usually not be considered acceptable by the end user.

    Is it mean: AQL 2.5 the same 2.5%?

  • http://www.qualityinspection.org/ Renaud Anjoran

    No it’s not. And it is now called “acceptance quality limit” in the standards. Not “acceptable” and not “quantity”.
    Besides the wrong name, the definition you got from that website is erroneous on several levels.

  • xuan

    Dear Mr Anjoran,
    Thank you for your explain.
    By the way, what’s different between general inspection level? and when do we use special inspection level S1,S2…..? Pls help me…

  • http://www.qualityinspection.org/ Renaud Anjoran
  • leslie

    Hi Anjoran!
    My company has an AQL for critical defect equal to 0.04%, major defect of 0.4% and minor defect of 1.5%. I just want to ask if you know what is the basis of this AQL and how they arrive with these. My company is bottling company producing alcoholic beverages

  • http://www.qualityinspection.org/ Renaud Anjoran

    Hi, as I wrote in this article, it is hard to base this on statistical reasoning and there is usually not definitive answer. I guess you should ask them…

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