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Unit 8: Acceptance Sampling

Lot Acceptance Sampling Notes
Dodge reasoned that a sample should be picked at random from the lot, and on the basis of
information that was yielded by the sample, a decision should be made regarding the disposition
of the lot. In general, the decision is either to accept or reject the lot. This process is called Lot
Acceptance Sampling or just Acceptance Sampling.
A point to remember is that the main purpose of acceptance sampling is to decide whether or not
the lot is likely to be acceptable, not to estimate the quality of the lot.

Scenarios Leading to Acceptance Sampling
Acceptance sampling is employed when one or several of the following hold:
1. Testing is destructive
2. The cost of 100% inspection is very high

3. 100% inspection takes too long

8.2 Acceptance Quality Control and Acceptance Sampling

It was pointed out by Harold Dodge in 1969 that Acceptance Quality Control is not the same as
Acceptance Sampling. The latter depends on specific sampling plans, which when implemented

indicate the conditions for acceptance or rejection of the immediate lot that is being inspected.
The former may be implemented in the form of an Acceptance Control Chart. The control limits
for the Acceptance Control Chart are computed using the specification limits and the standard

deviation of what is being monitored.
In 1942, Dodge stated: “..basically the “acceptance quality control” system that was developed
encompasses the concept of protecting the consumer from getting unacceptable defective product,
and encouraging the producer in the use of process quality control by: varying the quantity
and severity of acceptance inspections in direct relation to the importance of the characteristics
inspected, and in the inverse relation to the goodness of the quality level as indication by those
inspections.”
To reiterate the difference in these two approaches: acceptance sampling plans are one­shot deals,
which essentially test short­run effects. Quality control is of the long­run variety, and is part of a
well­designed system for lot acceptance.
Ed Schilling (1989) said: “An individual sampling plan has much the effect of a lone sniper, while
the sampling plan scheme can provide a fusillade in the battle for quality improvement.”
Control of Product Quality using Acceptance Control Charts

According to the ISO standard on acceptance control charts (ISO 7966, 1993), an acceptance control
chart combines consideration of control implications with elements of acceptance sampling. It is
an appropriate tool for helping to make decisions with respect to process acceptance.

The difference between acceptance sampling approaches and acceptance control
charts is the emphasis on process acceptability rather than on product disposition
decisions.

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