Effective Sampling

In order to judge the true characteristics of a lot---a collection of units of product---samples must be drawn at random, unless the lot requires 100% inspection. The unit refers to the unit of product (e.g. piece, set and box).

If one lot of cargo is stowed uniformly as in the Diagram: Sampling of Goods below, the inspector may use the random number based on the H-W-D (High-Wide-Deep). Referring to the diagram below, the H is 1 to 2, W is 1 to 3, and D is 1 to 2. The random number 1-3-1 is the box A, while 2-2-2 is the box B.

Assuming that a lot size---batch size or shipment size---to be inspected is 12 units and the required sample size is 3 units, the correct way to draw the samples is from all parts of the lot, for example, marked Right in the diagram. Drawing the samples from one segment only is incorrect, for example, marked Wrong in the diagram. It is incorrect to judge the true characteristics of a lot when the samples are drawn from a segment, row or corner.

In case of a full container load shipment, always inspect the goods before loading, not after loading. Accessibility is very important in random inspection. A lot size of one TEU (twenty-foot equivalent unit) may measure to 19' x 7.5' x 7.5' (5.79m x 2.29m x 2.29m). Despite its relatively large size, it is important to draw samples from different parts of the lot.

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