Acceptance Sampling: Definition, Methods, and Applications, Slides of Survey Sampling Techniques

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ACCEPTANCE

SAMPLING

SAMPLIN

G

Is the selection of a set of elements from a target population or product lot. Is frequently used because gathering data on every member of a target population or every product produced by a company is often impossible, impractical, or too costly to collect. It lets you draw conclusions or make inferences about the population or product lot from which the sample is draw

AVOIDING

SAMPLING

ERRORS

• (^) When used in

conjunction with

randomization, samples

provide virtually identical

characteristics relative to

those of the population or

product grouping from

which the sample was

drawn.

CATEGORIES OF SAMPLING ERRORS Bias (lack of accuracy) Dispersion (lack of precision) Non-reproducibility (lack of consistency)

HOW TO DETERMINE MINIMAL SAMPLING SIZES What confidence level is desired/specified The magnitude of the maximum allowable error (due to bias, dispersion, and/or non- reproducibility) The likelihood of occurrence of a specific event

KINDS OF INSPECTION 100% INSPECTION, ZERO INSPECTION OR ACCEPTANCE SAMPLING*.

WHEN IS IT APPLIED? When it has been demonstrated that the process that produced the batch comfortably meets the quality levels agreed between the customer and the supplier. It is also applied when the overall loss caused by defective units is small compared to the cost of sampling.

100% INSPECTION

• It consists of checking all items in the lot to remove those that do not comply with the established specifications.

WHEN IS IT APPLIED? It is used in cases where the products are high risk and if they are defective, a large economic loss can be generated. defective products can result in a large economic loss. It is also useful when the capacity of the batch manufacturing process is inadequate to meet specifications.

DISADVANTAGES There is a risk of monotony, more inspection errors and sometimes product damage. There are even cases where, due to the first two problems of 100% inspection, it is a policy that units are inspected twice (200% inspection).

WHEN

IS IT

USEFUL

When the inspection is carried out with destructive inspection by samples is indispensable, otherwise all products would be destroyed by the tests. When the cost of 100% inspection is too high compared to the cost of passing defective units. In cases where 100% inspection is technically or economically impossible.

WHEN IS IT USEFUL?

When the lot consists of many items to be inspected and

the probability of inspection error is sufficiently high that

100% inspection could miss more defective units than a

sampling plan.

In situations where, historically, the vendor has had

excellent quality levels and a reduction in the amount of

inspection is desired, but the process capability is not good

enough not to inspect.

Where there is a need to ensure product reliability, even

though the process capability of the batch manufacturer is

satisfactory.

BUT!

Acceptance

sampling gives

you no idea

about the

process that is

producing those

ítems!

e. g. Based on the information obtained from the inspection, a decision is made: to accept or reject the entire batch. A company receives a batch of materials or components from a certain supplier, a sample of items is selected from the batch and inspected according to certain quality criteria.