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Probability & Statistics

for Engineers & Scientists

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Probability & Statistics for Engineers & Scientists

N I N T H E D I T I O N

Ronald E. Walpole Roanoke College

Raymond H. Myers Virginia Tech

Sharon L. Myers Radford University

Keying Ye University of Texas at San Antonio

Prentice Hall

Editor in Chief: Deirdre Lynch Acquisitions Editor: Christopher Cummings Executive Content Editor: Christine O’Brien Associate Editor: Christina Lepre Senior Managing Editor: Karen Wernholm Senior Production Project Manager: Tracy Patruno Design Manager: Andrea Nix Cover Designer: Heather Scott Digital Assets Manager: Marianne Groth Associate Media Producer: Vicki Dreyfus Marketing Manager: Alex Gay Marketing Assistant: Kathleen DeChavez Senior Author Support/Technology Specialist: Joe Vetere Rights and Permissions Advisor: Michael Joyce Senior Manufacturing Buyer: Carol Melville Production Coordination: Lifland et al. Bookmakers Composition: Keying Ye Cover photo: Marjory Dressler/Dressler Photo-Graphics

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and Pearson was aware of a trademark claim, the designations have been printed in initial caps or all caps.

Library of Congress Cataloging-in-Publication Data

Probability & statistics for engineers & scientists/Ronald E. Walpole . . . [et al.] — 9th ed. p. cm. ISBN 978-0-321-62911-1 1. Engineering—Statistical methods. 2. Probabilities. I. Walpole, Ronald E.

TA340.P738 2011 519.02’462–dc22

2010004857

Copyright c⃝ 2012, 2007, 2002 Pearson Education, Inc. 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. For information on obtaining permission for use of material in this work, please submit a written request to Pearson Education, Inc., Rights and Contracts Department, 501 Boylston Street, Suite 900, Boston, MA 02116, fax your request to 617-671-3447, or e-mail at http://www.pearsoned.com/legal/permissions.htm.

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ISBN 10: 0-321-62911-6 ISBN 13: 978-0-321-62911-1

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This book is dedicated to

Billy and Julie

R.H.M. and S.L.M.

Limin, Carolyn and Emily

K.Y.

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Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

1 Introduction to Statistics and Data Analysis . . . . . . . . . . . 1 1.1 Overview: Statistical Inference, Samples, Populations, and the

Role of Probability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Sampling Procedures; Collection of Data . . . . . . . . . . . . . . . . . . . . . . . . 7

1.3 Measures of Location: The Sample Mean and Median . . . . . . . . . . . 11

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.4 Measures of Variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1.5 Discrete and Continuous Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1.6 Statistical Modeling, Scientific Inspection, and Graphical Diag-

nostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

1.7 General Types of Statistical Studies: Designed Experiment,

Observational Study, and Retrospective Study . . . . . . . . . . . . . . . . . . 27

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2 Probability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.1 Sample Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2.2 Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

2.3 Counting Sample Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

2.4 Probability of an Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

2.5 Additive Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

2.6 Conditional Probability, Independence, and the Product Rule . . . 62

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

2.7 Bayes’ Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

viii Contents

2.8 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

3 Random Variables and Probability Distributions . . . . . . 81 3.1 Concept of a Random Variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

3.2 Discrete Probability Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

3.3 Continuous Probability Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

3.4 Joint Probability Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

3.5 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

4 Mathematical Expectation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 4.1 Mean of a Random Variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

4.2 Variance and Covariance of Random Variables. . . . . . . . . . . . . . . . . . . 119

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

4.3 Means and Variances of Linear Combinations of Random Variables 128

4.4 Chebyshev’s Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

4.5 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

5 Some Discrete Probability Distributions . . . . . . . . . . . . . . . . 143 5.1 Introduction and Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

5.2 Binomial and Multinomial Distributions . . . . . . . . . . . . . . . . . . . . . . . . . 143

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

5.3 Hypergeometric Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

5.4 Negative Binomial and Geometric Distributions . . . . . . . . . . . . . . . . . 158

5.5 Poisson Distribution and the Poisson Process . . . . . . . . . . . . . . . . . . . . 161

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

5.6 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Contents ix

6 Some Continuous Probability Distributions . . . . . . . . . . . . . 171 6.1 Continuous Uniform Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

6.2 Normal Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

6.3 Areas under the Normal Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

6.4 Applications of the Normal Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 182

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

6.5 Normal Approximation to the Binomial . . . . . . . . . . . . . . . . . . . . . . . . . 187

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

6.6 Gamma and Exponential Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . 194

6.7 Chi-Squared Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

6.8 Beta Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

6.9 Lognormal Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

6.10 Weibull Distribution (Optional) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

6.11 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

7 Functions of Random Variables (Optional). . . . . . . . . . . . . . 211 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

7.2 Transformations of Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

7.3 Moments and Moment-Generating Functions . . . . . . . . . . . . . . . . . . . . 218

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

8 Fundamental Sampling Distributions and Data Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 8.1 Random Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

8.2 Some Important Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

8.3 Sampling Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

8.4 Sampling Distribution of Means and the Central Limit Theorem. 233

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

8.5 Sampling Distribution of S2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

8.6 t-Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

8.7 F -Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

8.8 Quantile and Probability Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

8.9 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

Sara

Sara

Sara

Sara

Sara

Sara

x Contents

9 One- and Two-Sample Estimation Problems . . . . . . . . . . . . 265 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

9.2 Statistical Inference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

9.3 Classical Methods of Estimation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266

9.4 Single Sample: Estimating the Mean . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

9.5 Standard Error of a Point Estimate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276

9.6 Prediction Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

9.7 Tolerance Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282

9.8 Two Samples: Estimating the Difference between Two Means . . . 285

9.9 Paired Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

9.10 Single Sample: Estimating a Proportion . . . . . . . . . . . . . . . . . . . . . . . . . 296

9.11 Two Samples: Estimating the Difference between Two Proportions 300

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

9.12 Single Sample: Estimating the Variance . . . . . . . . . . . . . . . . . . . . . . . . . 303

9.13 Two Samples: Estimating the Ratio of Two Variances . . . . . . . . . . . 305

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

9.14 Maximum Likelihood Estimation (Optional) . . . . . . . . . . . . . . . . . . . . . 307

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

9.15 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

10 One- and Two-Sample Tests of Hypotheses . . . . . . . . . . . . . 319 10.1 Statistical Hypotheses: General Concepts . . . . . . . . . . . . . . . . . . . . . . . 319

10.2 Testing a Statistical Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

10.3 The Use of P -Values for Decision Making in Testing Hypotheses . 331

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334

10.4 Single Sample: Tests Concerning a Single Mean . . . . . . . . . . . . . . . . . 336

10.5 Two Samples: Tests on Two Means . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

10.6 Choice of Sample Size for Testing Means . . . . . . . . . . . . . . . . . . . . . . . . 349

10.7 Graphical Methods for Comparing Means . . . . . . . . . . . . . . . . . . . . . . . 354

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356

10.8 One Sample: Test on a Single Proportion. . . . . . . . . . . . . . . . . . . . . . . . 360

10.9 Two Samples: Tests on Two Proportions . . . . . . . . . . . . . . . . . . . . . . . . 363

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

10.10 One- and Two-Sample Tests Concerning Variances . . . . . . . . . . . . . . 366

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

10.11 Goodness-of-Fit Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370

10.12 Test for Independence (Categorical Data) . . . . . . . . . . . . . . . . . . . . . . . 373

Contents xi

10.13 Test for Homogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376

10.14 Two-Sample Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

10.15 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386

11 Simple Linear Regression and Correlation . . . . . . . . . . . . . . 389 11.1 Introduction to Linear Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389

11.2 The Simple Linear Regression Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390

11.3 Least Squares and the Fitted Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

11.4 Properties of the Least Squares Estimators . . . . . . . . . . . . . . . . . . . . . . 400

11.5 Inferences Concerning the Regression Coefficients. . . . . . . . . . . . . . . . 403

11.6 Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

11.7 Choice of a Regression Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

11.8 Analysis-of-Variance Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

11.9 Test for Linearity of Regression: Data with Repeated Observations 416

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

11.10 Data Plots and Transformations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424

11.11 Simple Linear Regression Case Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . 428

11.12 Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436

11.13 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442

12 Multiple Linear Regression and Certain Nonlinear Regression Models . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443

12.2 Estimating the Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444

12.3 Linear Regression Model Using Matrices . . . . . . . . . . . . . . . . . . . . . . . . 447

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450

12.4 Properties of the Least Squares Estimators . . . . . . . . . . . . . . . . . . . . . . 453

12.5 Inferences in Multiple Linear Regression . . . . . . . . . . . . . . . . . . . . . . . . . 455

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461

12.6 Choice of a Fitted Model through Hypothesis Testing . . . . . . . . . . . 462

12.7 Special Case of Orthogonality (Optional) . . . . . . . . . . . . . . . . . . . . . . . . 467

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

12.8 Categorical or Indicator Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

xii Contents

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

12.9 Sequential Methods for Model Selection . . . . . . . . . . . . . . . . . . . . . . . . . 476

12.10 Study of Residuals and Violation of Assumptions (Model Check-

ing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

12.11 Cross Validation, Cp, and Other Criteria for Model Selection . . . . 487

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

12.12 Special Nonlinear Models for Nonideal Conditions . . . . . . . . . . . . . . . 496

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

12.13 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506

13 One-Factor Experiments: General . . . . . . . . . . . . . . . . . . . . . . . . 507 13.1 Analysis-of-Variance Technique. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507

13.2 The Strategy of Experimental Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . 508

13.3 One-Way Analysis of Variance: Completely Randomized Design

(One-Way ANOVA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509

13.4 Tests for the Equality of Several Variances . . . . . . . . . . . . . . . . . . . . . . 516

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518

13.5 Single-Degree-of-Freedom Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . 520

13.6 Multiple Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529

13.7 Comparing a Set of Treatments in Blocks . . . . . . . . . . . . . . . . . . . . . . . 532

13.8 Randomized Complete Block Designs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 533

13.9 Graphical Methods and Model Checking . . . . . . . . . . . . . . . . . . . . . . . . 540

13.10 Data Transformations in Analysis of Variance . . . . . . . . . . . . . . . . . . . 543

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545

13.11 Random Effects Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547

13.12 Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555

13.13 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559

14 Factorial Experiments (Two or More Factors) . . . . . . . . . . 561 14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

14.2 Interaction in the Two-Factor Experiment . . . . . . . . . . . . . . . . . . . . . . . 562

14.3 Two-Factor Analysis of Variance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575

14.4 Three-Factor Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586

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14.5 Factorial Experiments for Random Effects and Mixed Models. . . . 588

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594

14.6 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596

15 2k Factorial Experiments and Fractions . . . . . . . . . . . . . . . . . 597 15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597

15.2 The 2k Factorial: Calculation of Effects and Analysis of Variance 598

15.3 Nonreplicated 2k Factorial Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 604

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609

15.4 Factorial Experiments in a Regression Setting . . . . . . . . . . . . . . . . . . . 612

15.5 The Orthogonal Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625

15.6 Fractional Factorial Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626

15.7 Analysis of Fractional Factorial Experiments . . . . . . . . . . . . . . . . . . . . 632

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634

15.8 Higher Fractions and Screening Designs . . . . . . . . . . . . . . . . . . . . . . . . . 636

15.9 Construction of Resolution III and IV Designs with 8, 16, and 32

Design Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637

15.10 Other Two-Level Resolution III Designs; The Plackett-Burman

Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 638

15.11 Introduction to Response Surface Methodology . . . . . . . . . . . . . . . . . . 639

15.12 Robust Parameter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653

15.13 Potential Misconceptions and Hazards; Relationship to Material

in Other Chapters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654

16 Nonparametric Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655 16.1 Nonparametric Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655

16.2 Signed-Rank Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663

16.3 Wilcoxon Rank-Sum Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665

16.4 Kruskal-Wallis Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670

16.5 Runs Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671

16.6 Tolerance Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674

16.7 Rank Correlation Coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679

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17 Statistical Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681 17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681

17.2 Nature of the Control Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683

17.3 Purposes of the Control Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683

17.4 Control Charts for Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684

17.5 Control Charts for Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697

17.6 Cusum Control Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705

Review Exercises. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706

18 Bayesian Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709 18.1 Bayesian Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709

18.2 Bayesian Inferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710

18.3 Bayes Estimates Using Decision Theory Framework . . . . . . . . . . . . . 717

Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721

Appendix A: Statistical Tables and Proofs . . . . . . . . . . . . . . . . . . 725

Appendix B: Answers to Odd-Numbered Non-Review Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 769

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785

Preface

General Approach and Mathematical Level

Our emphasis in creating the ninth edition is less on adding new material and more on providing clarity and deeper understanding. This objective was accomplished in part by including new end-of-chapter material that adds connective tissue between chapters. We affectionately call these comments at the end of the chapter “Pot Holes.” They are very useful to remind students of the big picture and how each chapter fits into that picture, and they aid the student in learning about limitations and pitfalls that may result if procedures are misused. A deeper understanding of real-world use of statistics is made available through class projects, which were added in several chapters. These projects provide the opportunity for students alone, or in groups, to gather their own experimental data and draw inferences. In some cases, the work involves a problem whose solution will illustrate the meaning of a concept or provide an empirical understanding of an important statistical result. Some existing examples were expanded and new ones were introduced to create “case studies,” in which commentary is provided to give the student a clear understanding of a statistical concept in the context of a practical situation.

In this edition, we continue to emphasize a balance between theory and appli- cations. Calculus and other types of mathematical support (e.g., linear algebra) are used at about the same level as in previous editions. The coverage of an- alytical tools in statistics is enhanced with the use of calculus when discussion centers on rules and concepts in probability. Probability distributions and sta- tistical inference are highlighted in Chapters 2 through 10. Linear algebra and matrices are very lightly applied in Chapters 11 through 15, where linear regres- sion and analysis of variance are covered. Students using this text should have had the equivalent of one semester of differential and integral calculus. Linear algebra is helpful but not necessary so long as the section in Chapter 12 on mul- tiple linear regression using matrix algebra is not covered by the instructor. As in previous editions, a large number of exercises that deal with real-life scientific and engineering applications are available to challenge the student. The many data sets associated with the exercises are available for download from the website http://www.pearsonhighered.com/datasets.

xv

http://www.pearsonhighered.com/datasets

xvi Preface

Summary of the Changes in the Ninth Edition

• Class projects were added in several chapters to provide a deeper understand- ing of the real-world use of statistics. Students are asked to produce or gather their own experimental data and draw inferences from these data.

• More case studies were added and others expanded to help students under- stand the statistical methods being presented in the context of a real-life situ- ation. For example, the interpretation of confidence limits, prediction limits, and tolerance limits is given using a real-life situation.

• “Pot Holes” were added at the end of some chapters and expanded in others. These comments are intended to present each chapter in the context of the big picture and discuss how the chapters relate to one another. They also provide cautions about the possible misuse of statistical techniques presented in the chapter.

• Chapter 1 has been enhanced to include more on single-number statistics as well as graphical techniques. New fundamental material on sampling and experimental design is presented.

• Examples added to Chapter 8 on sampling distributions are intended to moti- vate P -values and hypothesis testing. This prepares the student for the more challenging material on these topics that will be presented in Chapter 10.

• Chapter 12 contains additional development regarding the effect of a single regression variable in a model in which collinearity with other variables is severe.

• Chapter 15 now introduces material on the important topic of response surface methodology (RSM). The use of noise variables in RSM allows the illustration of mean and variance (dual response surface) modeling.

• The central composite design (CCD) is introduced in Chapter 15. • More examples are given in Chapter 18, and the discussion of using Bayesian methods for statistical decision making has been enhanced.

Content and Course Planning

This text is designed for either a one- or a two-semester course. A reasonable plan for a one-semester course might include Chapters 1 through 10. This would result in a curriculum that concluded with the fundamentals of both estimation and hypothesis testing. Instructors who desire that students be exposed to simple linear regression may wish to include a portion of Chapter 11. For instructors who desire to have analysis of variance included rather than regression, the one- semester course may include Chapter 13 rather than Chapters 11 and 12. Chapter 13 features one-factor analysis of variance. Another option is to eliminate portions of Chapters 5 and/or 6 as well as Chapter 7. With this option, one or more of the discrete or continuous distributions in Chapters 5 and 6 may be eliminated. These distributions include the negative binomial, geometric, gamma, Weibull, beta, and log normal distributions. Other features that one might consider re- moving from a one-semester curriculum include maximum likelihood estimation,

Preface xvii

prediction, and/or tolerance limits in Chapter 9. A one-semester curriculum has built-in flexibility, depending on the relative interest of the instructor in regression, analysis of variance, experimental design, and response surface methods (Chapter 15). There are several discrete and continuous distributions (Chapters 5 and 6) that have applications in a variety of engineering and scientific areas.

Chapters 11 through 18 contain substantial material that can be added for the second semester of a two-semester course. The material on simple and multiple linear regression is in Chapters 11 and 12, respectively. Chapter 12 alone offers a substantial amount of flexibility. Multiple linear regression includes such “special topics” as categorical or indicator variables, sequential methods of model selection such as stepwise regression, the study of residuals for the detection of violations of assumptions, cross validation and the use of the PRESS statistic as well as Cp, and logistic regression. The use of orthogonal regressors, a precursor to the experimental design in Chapter 15, is highlighted. Chapters 13 and 14 offer a relatively large amount of material on analysis of variance (ANOVA) with fixed, random, and mixed models. Chapter 15 highlights the application of two-level designs in the context of full and fractional factorial experiments (2k). Special screening designs are illustrated. Chapter 15 also features a new section on response surface methodology (RSM) to illustrate the use of experimental design for finding optimal process conditions. The fitting of a second order model through the use of a central composite design is discussed. RSM is expanded to cover the analysis of robust parameter design type problems. Noise variables are used to accommodate dual response surface models. Chapters 16, 17, and 18 contain a moderate amount of material on nonparametric statistics, quality control, and Bayesian inference.

Chapter 1 is an overview of statistical inference presented on a mathematically simple level. It has been expanded from the eighth edition to more thoroughly cover single-number statistics and graphical techniques. It is designed to give students a preliminary presentation of elementary concepts that will allow them to understand more involved details that follow. Elementary concepts in sampling, data collection, and experimental design are presented, and rudimentary aspects of graphical tools are introduced, as well as a sense of what is garnered from a data set. Stem-and-leaf plots and box-and-whisker plots have been added. Graphs are better organized and labeled. The discussion of uncertainty and variation in a system is thorough and well illustrated. There are examples of how to sort out the important characteristics of a scientific process or system, and these ideas are illustrated in practical settings such as manufacturing processes, biomedical studies, and studies of biological and other scientific systems. A contrast is made between the use of discrete and continuous data. Emphasis is placed on the use of models and the information concerning statistical models that can be obtained from graphical tools.

Chapters 2, 3, and 4 deal with basic probability as well as discrete and contin- uous random variables. Chapters 5 and 6 focus on specific discrete and continuous distributions as well as relationships among them. These chapters also highlight examples of applications of the distributions in real-life scientific and engineering studies. Examples, case studies, and a large number of exercises edify the student concerning the use of these distributions. Projects bring the practical use of these distributions to life through group work. Chapter 7 is the most theoretical chapter

xviii Preface

in the text. It deals with transformation of random variables and will likely not be used unless the instructor wishes to teach a relatively theoretical course. Chapter 8 contains graphical material, expanding on the more elementary set of graphi- cal tools presented and illustrated in Chapter 1. Probability plotting is discussed and illustrated with examples. The very important concept of sampling distribu- tions is presented thoroughly, and illustrations are given that involve the central limit theorem and the distribution of a sample variance under normal, independent (i.i.d.) sampling. The t and F distributions are introduced to motivate their use in chapters to follow. New material in Chapter 8 helps the student to visualize the importance of hypothesis testing, motivating the concept of a P -value.

Chapter 9 contains material on one- and two-sample point and interval esti- mation. A thorough discussion with examples points out the contrast between the different types of intervals—confidence intervals, prediction intervals, and toler- ance intervals. A case study illustrates the three types of statistical intervals in the context of a manufacturing situation. This case study highlights the differences among the intervals, their sources, and the assumptions made in their develop- ment, as well as what type of scientific study or question requires the use of each one. A new approximation method has been added for the inference concerning a proportion. Chapter 10 begins with a basic presentation on the pragmatic mean- ing of hypothesis testing, with emphasis on such fundamental concepts as null and alternative hypotheses, the role of probability and the P -value, and the power of a test. Following this, illustrations are given of tests concerning one and two sam- ples under standard conditions. The two-sample t-test with paired observations is also described. A case study helps the student to develop a clear picture of what interaction among factors really means as well as the dangers that can arise when interaction between treatments and experimental units exists. At the end of Chapter 10 is a very important section that relates Chapters 9 and 10 (estimation and hypothesis testing) to Chapters 11 through 16, where statistical modeling is prominent. It is important that the student be aware of the strong connection.

Chapters 11 and 12 contain material on simple and multiple linear regression, respectively. Considerably more attention is given in this edition to the effect that collinearity among the regression variables plays. A situation is presented that shows how the role of a single regression variable can depend in large part on what regressors are in the model with it. The sequential model selection procedures (for- ward, backward, stepwise, etc.) are then revisited in regard to this concept, and the rationale for using certain P -values with these procedures is provided. Chap- ter 12 offers material on nonlinear modeling with a special presentation of logistic regression, which has applications in engineering and the biological sciences. The material on multiple regression is quite extensive and thus provides considerable flexibility for the instructor, as indicated earlier. At the end of Chapter 12 is com- mentary relating that chapter to Chapters 14 and 15. Several features were added that provide a better understanding of the material in general. For example, the end-of-chapter material deals with cautions and difficulties one might encounter. It is pointed out that there are types of responses that occur naturally in practice (e.g. proportion responses, count responses, and several others) with which stan- dard least squares regression should not be used because standard assumptions do not hold and violation of assumptions may induce serious errors. The suggestion is

Preface xix

made that data transformation on the response may alleviate the problem in some cases. Flexibility is again available in Chapters 13 and 14, on the topic of analysis of variance. Chapter 13 covers one-factor ANOVA in the context of a completely randomized design. Complementary topics include tests on variances and multiple comparisons. Comparisons of treatments in blocks are highlighted, along with the topic of randomized complete blocks. Graphical methods are extended to ANOVA to aid the student in supplementing the formal inference with a pictorial type of in- ference that can aid scientists and engineers in presenting material. A new project is given in which students incorporate the appropriate randomization into each plan and use graphical techniques and P -values in reporting the results. Chapter 14 extends the material in Chapter 13 to accommodate two or more factors that are in a factorial structure. The ANOVA presentation in Chapter 14 includes work in both random and fixed effects models. Chapter 15 offers material associated with 2k factorial designs; examples and case studies present the use of screening designs and special higher fractions of the 2k. Two new and special features are the presentations of response surface methodology (RSM) and robust parameter design. These topics are linked in a case study that describes and illustrates a dual response surface design and analysis featuring the use of process mean and variance response surfaces.