What is the difference between statistical quality control and unprofessional inspections? A professional inspector will follow a valid sampling plan.
A sampling plan should take care of three fundamental concerns:
- There should be a clear limit between acceptability and refusal,
- This limit should be set before inspection starts (actually, even before production starts) and be transparent for the supplier,
- The inspection’s conclusions should be applicable (with a certain degree of confidence) to the whole order quantity–not just to the few samples that were checked.
The problem: no user-friendly tool
The quality control industry in Asia uses the same statistical tools. They were set as standards by the US army during World War II (to check the army’s procurements), and they were more recently taken over by “commercial” institutes such as ISO, ASQ, etc.
Everybody calls them the AQL tables (one of many jargon terms of the QC industry). The AQL tables are very functional for everyday users, but they are a real put off for buyers and suppliers.
I read that Google did a survey and found that only 8% of pedestrians in Manhattan knew exactly what a “browser” is. In the same way, I bet that less than 5% of purchasers know how their inspectors choose a sampling plan. And even less have a clear understanding of the impact of a difference in inspection level of in AQL.
An easier way to get a sampling plan
I came upon one or two online tools to calculate the number of samples and the AQL limits, but they are not really adapted to quality control in the context of international trade. And all they give is numbers, not explanations.
So we developed a very simple tool to get a rigorous plan and to understand how to apply it:
[Update: we have "killed" this feature. Sorry!]
I hope many readers will use it and will spread the word. Any suggestions to make it better or more convenient?