Lecture Operations management: Creating value along the supply chain (Canadian edition) - Chapter 3S

OPERATIONS MANAGEMENT:
Creating Value Along the Supply Chain,
Canadian Edition
Robert S. Russell, Bernard W. Taylor III, Ignacio Castillo, Navneet Vidyarthi

CHAPTER 3 SUPPLEMENT
Acceptance Sampling

Supplement 3-1


Lecture Outline
—Single-Sample Attribute Plan
—Operating Characteristic Curve
—Developing a Sampling Plan with Excel
—Average Outgoing Quality
—Double - and Multiple-Sampling Plans

Supplement 3-2


Acceptance Sampling
—Accepting or rejecting a production lot 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
—Sampling plan
—provides guidelines for accepting a lot

Supplement 3-3


Single–Sample Attribute Plan

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Single sampling plan
•
•
•
•

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N = lot size
n = sample size (random)
c = acceptance number
d = number of defective items in sample

If d ≤c, accept lot; else reject

Supplement 3-4

Producer’s and Consumer’s Risk
—AQL or acceptable quality level
—proportion of defects consumer will accept in given lot
— or producer’s risk
—probability of rejecting a good lot

—LTPD or lot tolerance percent defective
—limit on the number of defectives the customer will accept
—β or consumer’s risk
—probability of accepting a bad lot

Supplement 3-5


Producer’s and Consumer’s Risk

Good Lot

Reject

No Error

Type I Error
Producer’ Risk

Bad Lot

Accept

Type II Error

Consumer’s Risk

No Error

Sampling Errors

Supplement 3-6


Operating Characteristic (OC) Curve
—Shows probability of accepting lots of different

quality levels with 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) and acceptance level (c) for the
sampling plan

Supplement 3-7


OC Curve

Supplement 3-8


Developing a Sampling Plan
with OM Tools
ABC Company produces mugs in lots of 10,000.

Quality contracts require producer’s risk of 0.05 with
an AQL of 1% defective and a consumer’s risk of
0.10 with a LTPD of 5% defective. What size
sample and what acceptance number should ABC
use to achieve performance measures called for in
the sampling plan?

N = 10,000
α = 0.05
β = 0.10
AQL = 1%
LTPD = 5%
n=?
C=?

Supplement 3-9


Average Outgoing Quality (AOQ)
—Expected number of defective items that will pass

on to customer with a sampling plan
—Average outgoing quality limit (AOQL)
—maximum point on the curve
—worst level of outgoing quality

Supplement 3-10


AOQ Curve

Supplement 3-11


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

Supplement 3-12


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 reject lot based

on all sample data

Supplement 3-13

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