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Copyright 2006 John Wiley & Sons, Inc.Beni Asllani

University of Tennessee at Chattanooga

Operations Management - 5thEdition

Chapter 4 Supplement

Roberta Russell & Bernard W. Taylor, III

Acceptance Sampling

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Copyright 2006 John Wiley & Sons, Inc. Supplement 4-2

Lecture Outline

Single-Sample Attribute Plan

Operating Characteristic Curve

Developing a Sampling Plan with Excel

Average Outgoing Quality

Double - and Multiple-Sampling Plans

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Acceptance Sampling

Accepting or rejecting a productionlot based on the number of defects

in a sample Not consistent with TQM or Zero

Defects philosophy producer and customer agree on the

number of acceptable defects a means of identifying not preventing

poor quality percent of defective parts versus PPM

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SingleSample

Attribute Plan

Single sampling plan

N= lot size

n= sample size (random)

c= acceptance number

d= number of defective items in sample

If d c, accept lot; else reject

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Producers and

Consumers Risk AQL or acceptable quality level

proportion defect the customer will accept a

given lot LTPD or lot tolerance percent defective

limit on the number of defectives thecustomer will accept

or producers risk probability of rejecting a good lot or consumers risk

probability of accepting a bad lot

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Copyright 2006 John Wiley & Sons, Inc. Supplement 4-6

Producers and

Consumers Risk (cont.)

Sampling Errors

GoodLot

Bad

Lot

Accept Reject

No Error Type I ErrorProducer Risk

Type II Error

Consumers RiskNo Error

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Operating Characteristic

(OC) Curve shows probability of accepting lots of

different quality levels for a specific

sampling plan assists management to discriminate

between good and bad lots

exact shape and location of the curve is

defined by the sample size (n) andacceptance level (c) for the samplingplan

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OC Curve (cont.)

OC curve forn

andc

Proportion defectiveAQL LTPD

Probabilityofaccep

tance,

Pa

= 0.10

= 0.051.00

0.80

0.60

0.40

0.20

|0.02

|

0.04

|

0.06

|

0.08

|

0.10

|

0.12

|

0.14

|

0.16

|

0.18

|

0.20

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Developing a Sampling Plan

with Excel

ABC Company produces mugs inlots of 10,000. Performancemeasures for quality of mugs sentto stores call for a producers riskof 0.05 with an AQL of 1%defective and a consumers risk of0.10 with a LTPD of 5% defective.What size sample and whatacceptance number should ABCuse to achieve performancemeasures called for in the sampling

plan?

N = 10,000 n = ?

= 0.05 c = ? = 0.10

AQL = 1%

LTPD = 5%

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Sampling Plan and OC Curve

Input

Use Poisson

distribution functionto calculate PAs

Use chart wizard to

graph OC

Use Solver to find

values forn and c

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Average Outgoing

Quality (AOQ)

Expected number of defective

items that will pass on tocustomer with a sampling plan

Average outgoing quality limit

(AOQL) maximum point on the curve

worst level of outgoing quality

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AOQ Curve

AOQL 1.39%

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Double Sampling Plans

Take small initial sample If # defective < lower limit, accept

If # defective > upper limit, reject If # defective between limits, take second

sample

Accept or reject based on 2 samples

Less costly than single-sampling plans

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Multiple Sampling Plans

Uses smaller sample sizes

Take initial sample If # defective < lower limit, accept

If # defective > upper limit, reject

If # defective between limits, resample

Continue sampling until accept or rejectlot based on all sample data

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Copyright 2006 John Wiley & Sons, Inc.

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