McGraw-Hill/Irwin Copyright © 2007 by The McGraw-Hill Companies, Inc. All rights reserved. 10S Acceptance Sampling

10S-2 Learning Objectives  Explain the purpose of acceptance sampling  Contrast acceptance sampling and process control  Compare and contrast single- and multiple- sampling plans  Determine the average outgoing quality of inspected lots

10S-3 Sampling Plans  Acceptance sampling : Form of inspection applied to lots or batches of items before or after a process, to judge conformance with predetermined standards  Sampling plans: Plans that specify lot size, sample size, number of samples, and acceptance/rejection criteria  Single-sampling  Double-sampling  Multiple-sampling

10S-4 Acceptance Sampling  Acceptance Sampling most useful when  A large number of items must be processed in a short time  The cost consequences of passing defects are low  Destructive testing is required  Fatigue or boredom leads to inspection errors

10S-5 Operating Characteristic Curve  Operating Characteristic (OC) Curve: Probability curve that shows the probabilities of accepting lots with various fractions defective.

10S-6 Typical OC Curve Probability of accepting lot Lot quality (fraction defective) 3% Figure 10S.1

10S-7 Decision Criteria Probability of accepting lot Lot quality (fraction defective) “Good”“Bad” Ideal Not very discriminating Figure 10S.2

10S-8 Sampling Terms  Acceptance quality level (AQL): the percentage 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  Consumer’s risk: the probability that a lot contained defectives exceeding the LTPD will be accepted  Producer’s risk: the probability that a lot containing the acceptable quality level will be rejected

10S-9 Consumer’s and Producer’s Risk Probability of accepting lot Lot quality (fraction defective)  =.10  =.10 “Good” AQL “Bad”Indifferent LTPD Figure 10S.3

10S-10 QC Curve for n = 10, c = 1 Figure 10S Probability of acceptance Fraction defective in lot

10S-11 Average Quality  Average outgoing quality (AOQ): Average of inspected lots (100%) and uninspected lots Pac = Probability of accepting lot p= Fraction defective N= Lot size n= Sample size

10S-12 Example S-2: AOQ Approximate AOQL =.082 AOQ (Fraction defective out) Incoming fraction defective