Acceptance Sampling Copyright © 2015 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

10S-2 You should be able to: LO 10S.1Explain the purpose of acceptance sampling LO 10S.2Compare and contrast single- and multiple- sampling plans LO 10S.3Describe what an operating characteristic curve does LO 10S.4Determine the average outgoing quality of inspected lots

10S-3 Acceptance sampling A form of inspection applied to lots or batches of items before or after a process, to judge conformance with predetermined standards May be applied to both attribute and variable inspection LO 10S.1

10S-4 The purpose of acceptance sampling is to decide whether a lot satisfies predetermined standards Lots that satisfy these standards are passed or accepted Rejected lots may be subjected to 100 percent inspection In the case of purchased goods, they may be returned for credit or replacement LO 10S.1

10S-5 Single-sampling plan One random sample is drawn from each lot Every item in the sample is inspected and classified as “good” or “defective” If any sample contains more than a specified number of defectives, c, the lot is rejected LO 10S.2

10S-6 Double-Sampling Plan Allows the opportunity to take a second sample if the results of the initial sample are inconclusive Two values are specified for the number of defective items A lower level, c 1 An upper level, c 2 If the number of defectives in the first sample is ≤ c 1 the lot is accepted and sampling is terminated > c 2 the lot is rejected and sampling is terminated Between c 1 and c 2 a second sample is collected The number of defectives in both samples is compared to a third value, c 3 If the combined number of defectives does not exceed this value, the lot is accepted; otherwise, it is rejected LO 10S.2

10S-7 Multiple-sampling plan Similar to a double-sampling plan except more than two samples may be required A sampling plan will specify each sample size and two limits for each sample The limit values increase with the number of samples If, for any sample, the cumulative number of defectives found exceeds the upper limit specified, the lot is rejected If for any sample the cumulative number of defectives found is less than or equal to the lower limit, the lot is accepted. If the number of defectives found is between the two limits, another sample is taken The process continues until the lot is accepted or rejected LO 10S.2

10S-8 An important sampling plan characteristic is how it discriminates between high and low quality OC curves describe a sampling plan’s ability to discriminate OC curve Probability curve that shows the probabilities of accepting lots with various fractions defective LO 10S.3

10S-9 A typical OC Curve for Proportions LO 10S.3

10S-10 Acceptable quality Level (AQL) The percentage level of defects at which consumers are willing to accept lots as “good” Lot tolerance percent defective (LTPD) The upper limit on the percentage of defects that a consumer is willing to accept LO 10S.3

10S-11 The AQL indicates good lots, and the LTPD indicates bad lots LO 10S.3

10S-12 An interesting feature of acceptance sampling is that the level of inspection automatically adjusts to the quality of the lots being inspected, assuming rejected lots are subjected to 100 percent inspection Good lots have a high probability and bad lots a low probability of being accepted. If the lots inspected are mostly good, few will end up going through 100 percent inspection. The poorer the quality of the lots, the greater the number of lots that will come under close scrutiny LO 10S.4

10S-13 Average outgoing quality Average of rejected lots (100 percent inspection) and accepted lots (a sample of items inspected) LO 10S.4

10S-14 In practice, the last term of the AOQ formula is close to 1.0 Eliminate this term, so Construct the AOQ curve for this situation N = 500, n = 10, and c = 1 p p ac AOQ LO 10S.4

10S-15 Approximate AOQ =.082 LO 10S.4