Page 230 - DMGT501_OPERATIONS_MANAGEMENT

Operations Management

Notes 8.3 Lot Acceptance Sampling Plans (LASPs)

LASP is a sampling scheme and a set of rules A Lot Acceptance Sampling Plan (LASP) is a
sampling scheme and a set of rules for making decisions. The decision, based on counting the
number of defectives in a sample, can be to accept the lot, reject the lot, or even, for multiple or
sequential sampling schemes, to take another sample and then repeat the decision process.

Types of LASPs

Types of acceptance plans to choose from LASPs fall into the following categories:
1. Single sampling plans: One sample of items is selected at random from a lot and the
disposition of the lot is determined from the resulting information. These plans are usually
denoted as (n,c) plans for a sample size n, where the lot is rejected if there are more than
c defectives. These are the most common (and easiest) plans to use although not the most

efficient in terms of average number of samples needed.
2. Double sampling plans: After the first sample is tested, there are three possibilities:

(a) Accept the lot
(b) Reject the lot
(c) No decision

If the outcome is (3), and a second sample is taken, the procedure is to combine the results of both
samples and make a final decision based on that information.

1. Multiple sampling plans: This is an extension of the double sampling plans where more
than two samples are needed to reach a conclusion. The advantage of multiple sampling is
smaller sample sizes.

2. Sequential sampling plans: This is the ultimate extension of multiple sampling where items
are selected from a lot one at a time and after inspection of each item a decision is made to
accept or reject the lot or select another unit.
3. Skip lot sampling plans: Skip lot sampling means that only a fraction of the submitted lots
are inspected.

Definitions of basic Acceptance Sampling terms: Deriving a plan, within one of the categories

listed above is discussed later. All derivations depend on the properties you want the plan to
have. These are described using the following terms:
1. Acceptable Quality Level (AQL): The AQL is a percent defective that is the base line
requirement for the quality of the producer’s product. The producer would like to design a
sampling plan such that there is a high probability of accepting a lot that has a defect level
less than or equal to the AQL.

2. Lot Tolerance Percent Defective (LTPD): The LTPD is a designated high defect level that
would be unacceptable to the consumer. The consumer would like the sampling plan to
have a low probability of accepting a lot with a defect level as high as the LTPD.
3. Type I Error (Producer’s Risk): This is the probability, for a given (n,c) sampling plan, of
rejecting a lot that has a defect level equal to the AQL. The producer suffers when this
occurs, because a lot with acceptable quality was rejected. The symbol is commonly used
for the Type I error and typical values for range from 0.2 to 0.01.

4. Type II Error (Consumer’s Risk): This is the probability, for a given (n,c) sampling plan,
of accepting a lot with a defect level equal to the LTPD. The consumer suffers when this

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