managing quality integrating the supply chain - 4th edition
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Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11 - 1
Chapter 11Statistically-Based
Quality Improvement for Variables
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 2
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesChapter 11
Statistical FundamentalsControl ChartsSome Control Chart Concepts for VariablesProcess Capability for VariablesA Closer Look at QualityOther Statistical Techniques in Quality Management
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 3
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Statistical ThinkingAll work occurs in a system of interconnected processesAll process have variation (The amount … tends to be underestimated)Understanding variation and reducing variation are important keys to success
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 4
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Why do statistics sometimes fail in the workplace?Lack of knowledge about the toolsGeneral disdain for all things mathematicalCultural barriers in a companyStatistical specialists have trouble communicating
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 5
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Why do statistics sometimes fail in the workplace?Statistics generally are poorly taught, emphasizing mathematical development rather than applicationPeople have a poor understanding of the scientific method
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 6
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Why do statistics sometimes fail in the workplace?Organizations lack patience in collecting data. All decisions have to be made “yesterday”Statistics are viewed as something to buttress an already-held opinionPeople fear using statistics
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 7
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Why do statistics sometimes fail in the workplace?Most people don’t understand random variationStatistical tools often are reactive and focus on effects rather than causes
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 8
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Type I and Type II Errors Type I error
Producers riskProbability that a good product will be rejected
Type II errorConsumers riskProbability that a nonconforming product will be available for sale
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 9
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Understanding Process VariationRandom variation
Centered around the meanConsistent amount of dispersion
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 10
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Understanding Process VariationNonrandom variation
“Special Causes”Results from some eventDispersion and average of the process are changing Process that is not repeatable
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 11
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Understanding Process VariationProcess stability
Random VariationNot nonrandom variationProcess Charts
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 12
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Understanding Process VariationSampling Methods
Samples are cheaperTake less timeLess intrusiveDestructive tests may destroy the sample
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 13
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Random Samples Each piece has an equal chance of being selected for inspection
Systematic SamplesAccording to time or sequence
Rational subgroupsA group of data that is logically homogeneousComputing variation between subgroups
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 14
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesStatistical Fundamentals
Planning for InspectionWhat type of planning will be usedWho will perform the inspectionWhat critical attributes to be inspected are
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 15
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesControl Charts
Variables and attributes control charts
1. You must understand this generic process for implementing process charts
2. You must know how to interpret process charts
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 16
Strategic Quality PlanningStatistically-Based Quality Improvement for Variables Control Charts
Variables and attributes control charts
3. You need to know when different process charts are used
4. You need to know how to computer limits for the different type of process chart
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 17
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesControl Charts
A generalized procedure for developing process charts
1. Identify critical operations in the process
2. Identify critical product characteristics3. Determine whether the critical
product characteristic is a variable or an attribute
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 18
Strategic Quality PlanningStatistically-Based Quality Improvement for Variables Control Charts
A generalized procedure for developing process charts
4. Select the appropriate process control chart
5. Establish the control limits and use the chart to continually monitor and improve
6. Update the limits when changes have been made to the process
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 19
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesControl Charts
Understanding control chartsA control chart is an application of
hypothesis testing where:The null hypothesis is that the process is
stable
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 20
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesSome Control Chart Concepts for Variables
Choosing the correct variables control chart
Are the data variable? Is it homogeneous in nature or not
conducive to subgroup sampling?
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 21
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesSome Control Chart Concepts for Variables
When a process is out of control some corrective action is needed:
1. Identify the quality problem2. Form the correct team to evaluate
and solve the problem3. Use structured brainstorming4. Brainstorm to identify potential
solutions
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 22
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesSome Control Chart Concepts for Variables
When a process is out of control some corrective action is needed:
5. Eliminate the cause6. Restart the process7. Document the problem, root cause
and solutions8. Communicate the results
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 23
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesProcess Capability for Variables
A highly capable process produces high volumes with few or no defects
World-class levels of process capability are measured by parts per million (ppm) defect levels
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 24
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesProcess Capability for Variables
Six Sigma
A design program which emphasized engineering parts so that they are highly capable
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 25
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesProcess Capability for Variables
Capability Studies Two purposes to determine whether
a process is capable1. To determine whether a process
consistently results in products that meet specifications
2. To determine whether a is in need of monitoring
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 26
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesProcess Capability for Variables
The difference between capability and stability
A process is capable if individual products consistently meet specification
A process is stable only if common variation is present in the process
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall. 11- 27
Strategic Quality PlanningStatistically-Based Quality Improvement for VariablesSummary
You need: To know the generic process for
developing charts To be able to interpret charts To be able to choose which chart to
use The formulas to derive the charts To understand the purposes and
assumptions underlying the charts
11- 28Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying,
recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America.
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