Inspection Levels

What are inspection levels? As an importer of global trading business, maybe you let your supplier ship the goods without inspecting. Maybe you use a third-party agent to control your production. Or maybe you have your own QC inspectors. But have you ever thought about you are taking unnecessary risks? Are you paying too much? The only way to form an opinion about these questions is to be familiar with the basics of quality control.

Military Standard 105 was created and used by the US Department of Defense to control their procurements more efficiently. In 1994 they decided to rely on non-governmental organizations to maintain this type of standard. The ANSI, ISO, BS and other institutes all created their own standard, but in essence they are similar to the latest version of Mlt-Std 105E. All third-party QC firms use the same standards and the same statistical tables. That is now we are using and called ANSI/ASQ Z1.4

Why use random sampling?

Shipments often represent thousands of products. Full inspection/100% inspection of the quantity would be long and expensive. A solution is to select samples at random and inspect them, instead of checking the whole lot. But how many samples to select? On one hand, checking only a few pieces might prevent the inspector from noticing quality issues; on the other hand, the objective is to keep the inspection short by reducing the number of samples to check. The relevant standards propose a standard severity, called “normal level” or “level II”. It is designed to balance these two imperatives in the most efficient manner, and it is used for more than 80% of inspections. For examples, for an order of 5,000 products, only 200 samples are inspected, while for an order of 30,000 products, only 315 samples are inspected.

When to switch to tightened or reduced inspection levels?

Suppose you source a product from a factory that often ships substandard quality. You know that the risk is higher than average. How to increase the discriminating power of the inspection? You can opt for the “tightened level” (level III) and more samples are checked. Similarly, if a supplier has consistently delivered acceptable products in the past and keeps using the same workshop, you can choose the “reduced level” (level I). As fewer samples have to be checked, the inspection might take less time and be cheaper. In practice, the relevant standards give very precise guidelines about when to switch, but most importers rely on their “gut feeling”. If you want to respect these guidelines strictly, ask your QC manager or your external inspection provider.

The “Special Levels”

Inspectors frequently have to perform some special tests on the products they are checking. In some cases the tests can only be performed on very few samples, for two reasons:

• They might take a long time (e.g. doing a full function test as per claims on the retail box).
• They end up in product destruction. (e.g. Opening the tins to check the content of can food). For these situations only, the clientcan choose a “special level”.

So we have three “general” inspection levels, and four “special levels”. For a given order quantity, each level gives a different number of samples to check. You can decide on which level to use for a specific order of products and quantity.