One of the common tools of quality assurance is acceptance sampling. Acceptance sampling uses the observed properties of a sample drawn from a lot or batch to make a decision about whether to accept or reject that lot or batch. Textbooks are full of complex descriptions of various acceptance sampling plans, however, there are some very important aspects of acceptance sampling that are not included in the textbooks. These are the topic of this column.

Extrapolation

In the interest of simplicity, the product that has been measured will be referred to as the “sample,” while the product that has not been measured will be referred to as the “lot.” Every time that we attempt to use a sample to characterize the conformity of a lot, we will be making an extrapolation from the product that has been measured to the product that has not been measured. Now extrapolation is beyond the scope of most courses of instruction and education simply because it is so complex. Yet, typically, it is the one thing that we are called on to do on a daily basis. So how can we extrapolate from the sample to the lot?

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