How AQL Inspection Levels Impact Your Sampling Size
By Space Coast Daily // March 12, 2023
Many people have misconceptions about the quality control industry, primarily overseeing product quality in China. Many importers believe that before shipping an order, they must inspect each piece of each Stock Keeping Unit (SKU) in the lot.
For some high-value products and buyers, it may be required to check the entirety of an order. For many importers of consumer goods, it is usually more cost-effective to inspect a random sample of the order.
Most importers lack legal expertise in the statistical models required for determining the proper sample sizes. Acceptable quality levels (AQL), also known as acceptable quality limits, are a QC sampling methodology that is straightforward to apply and doesn’t require any background knowledge.
This article explores how AQL Inspection Levels impact your sampling size, the three AQL inspection levels, and other relevant areas.
How AQL Inspection Levels Impact Your Sampling Size
Acceptance sampling, a statistical approach to quality control sampling that helps determine whether to reject or accept a production lot based on representative sample size, is the foundation of AQL.
The worst or lowest quality level, or limit, allowed in the order of goods is generally referred to as the AQL. This is often measured by the number of units with quality flaws or defects detected in the inspected sample size. And this ratio of detected defects to the total sample size aids in determining whether or not the order passes inspection.
Using the wrong sample size for inspection can lead to the following two potential issues:
- Inspecting insufficient pieces to determine the total order properly: You risk discovering more problems than expected based on the inspection result after receiving the entire shipment at your warehouse.
- Inspecting more components than necessary to precisely determine the entire order: This may increase your quality control expenses and cause production or shipping delays.
What AQL Standard Is The Most Appropriate For You?
ANSI-ASQ Z.14 is the most popular AQL standard for the consumer goods sector. The American Society for Quality (ASQ) and the American National Standards Institute (ANSI) developed ANSI-ASQ Z.14 (ASQ).
With the aid of the ANSI-ASQ Z.14 AQL table, you can:
- Depending on your lot size, determine the proper sample size you should inspect.
- Your AQL, defect tolerance, or the maximum number of flaws you will accept in the order, also referred to as a “accept point.”
By being aware of these, you can decide whether to reject or accept the entire lot based on the findings of a sample inspection.
But how large of a sample size should you use? The sample sizes listed in the AQL table range slightly in size and risk. Even with the statistical validity of all sample sizes, some will offer a better understanding of order quality than others. It’s up to you to decide on the sample size you want based on how much risk you’re willing to take.
How can you determine which sample size best suits your budget, order, and risk tolerance? Let’s examine the AQL inspection levels in more detail.
The Three AQL General Inspection Levels
“GI,” “GII,” and “GIII” are the three general AQL inspection levels. Each one represents the non-destructive inspection sample sizes.
GI Inspection Level
The GI inspection level gives the fewest sample sizes of the three general inspection levels. GI is regarded as the “budget option,” so if money or time is scarce, it might be your best choice.
GI might be adequate in the following cases:
- Your limited resources prevent you from sending an inspector to conduct a comprehensive inspection beyond one day.
- Products such as promotional goods are inexpensive or have negligible safety risks.
- Suppliers have a proven track record of satisfying your standards and a robust quality management system (QMS) based on ISO 9001.
GII Inspection Level
Inspection firms commonly refer to the GII AQL inspection level as a “normal” sample size. The inspection level importers select most frequently is GII because it offers an enormous covering scope at a reasonable price.
The GII inspection level is frequently very appropriate during the initial lot inspection. Seeing these preliminary findings can aid you in deciding whether GII is still proper moving ahead or whether you should raise or reduce your inspection level.
Assuming your acceptable quality levels maintain the same, the accept and reject scores often rise with the sample size. As a result, your accept point increases to 10 defects with an AQL of 2.5, while your reject point rises to 11 defects.
GIII Inspection Level
Of the three AQL inspection levels, the GIII inspection level offers the largest sample size for your lot. The GIII sample size is roughly four times as big—315 pieces—compared to the GI sample size, which is 80 units for a 5,000-piece lot size.
With acceptance sampling, this general inspection level provides the most excellent assurance and broadest coverage of order status and quality. GIII reduces your chance of accidentally accepting a shipment that has more damaged items than were discovered during an inspection.
A GIII sample size of 315 pieces, using your 5,000-piece lot size as an example, would result in a reject point of 15 defects and an accept point of 14 defects.
Some purchasers are under the impression that before shipment, they must check the quality of each item in a lot. More product inspections can also bring about greater transparency. Yet, you may frequently obtain sufficient data from a random, smaller sample to make an informed choice for the entire order.
Your particular set of conditions will determine which quality control sampling technique or sample size you choose for inspection. When selecting the best AQL inspection levels for your order, carefully evaluate your budget, the type of goods, and your supplier’s history.
And keep in mind that maintaining product quality is a continuous effort. Throughout your engagement with your supplier, don’t hesitate to modify your acceptable quality levels to better suit your changing demands and circumstances.
In all, EC Global Inspection is your sure plug regarding how AQL inspection levels impact your sampling size.