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Chapter 15
B. Sampling
Define and interpret terms such as
acceptable quality level (AQL), random
sampling, lot size, acceptance number,
sampling plans, inspection type, timeliness,
etc. (Application)
Body of Knowledge III.B
Part III.B
INTRODUCTION
Acceptance sampling is a method for inspecting product. Inspection can be
done with screening (also called sorting or 100 percent inspection), in which all
units are inspected, or with sampling. Acceptance sampling is the process of
inspecting a portion of the product in a lot for the purpose of making a decision
regarding classification of the entire lot as either conforming or nonconforming to
quality specifications.
Whether inspection is done with screening or with sampling, the results of
inspection can be used for different purposes as follows:
1. To distinguish between good lots and bad lots, using acceptance sampling
plans (as in incoming material inspection and final product inspection).
2. To distinguish between good products and bad products.
3. To determine the status of process control and whether the process is changing.
This is usually done with control charts.
4. To evaluate process capability. In this case, inspection is used to determine
whether the process exhibits excessive variation and whether it is
approaching or exceeding the specification limits.
5. To determine process adjustment. Based on inspection results of process
output, as depicted by a histogram for example, the process mean
may require adjustment and/or process variation may need to be
reduced. A process might require adjustment even though all the
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