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Cover image for The multivariate solution to statistical process control : qualstat 3
Title:
The multivariate solution to statistical process control : qualstat 3
Personal Author:
Series:
ASA-SIAM series on statistics and applied probability
Publication Information:
Philadelphia, PA : Society for Industrial and Applied Mathematics, 2002
Physical Description:
1 CD-ROM ; 12 cm
ISBN:
9780898714968
General Note:
Accompanies text entitled : Multivariate statistical process control with industrial applications (TS156.8 M37 2002)
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Summary

Summary

This applied, self-contained text provides detailed coverage of the practical aspects of multivariate statistical process control (MVSPC) based on the application of Hotelling's T2 statistic. MVSPC is the application of multivariate statistical techniques to improve the quality and productivity of an industrial process. The authors, leading researchers in this area who have developed major software for this type of charting procedure, provide valuable insight into the T2 statistic. Intentionally including only a minimal amount of theory, they lead readers through the construction and monitoring phases of the T2 control statistic using numerous industrial examples taken primarily from the chemical and power industries. These examples are applied to the construction of historical data sets to serve as a point of reference for the control procedure and are also applied to the monitoring phase, where emphasis is placed on signal location and interpretation in terms of the process variables.

Specifically devoted to the T2 methodology, this is the only book available that concisely and thoroughly presents such topics as how to construct a historical data set; how to check the necessary assumptions used with this procedure; how to chart the T2 statistic; how to interpret its signals; how to use the chart in the presence of autocorrelated data; and how to apply the procedure to batch processes. The book comes with a CD-ROM containing a 90-day demonstration version of the QualStat™ multivariate SPC software specifically designed for the application of T2 control procedures. The CD-ROM is compatible with Windows® 95, Windows® 98, Windows® Me Millennium Edition, and Windows NT® operating systems.


Author Notes

Robert L. Mason is a Staff Analyst at the Southwest Research Institute in San Antonio, Texas. He is a fellow of both the American Statistical Association and the American Society for Quality
John C. Young is a Professor of Statistics at McNeese State University in Lake Charles, Louisiana


Table of Contents

Prefacep. xi
1 Introduction to the T[superscript 2] Statisticp. 1
1.1 Introductionp. 3
1.2 Univariate Control Proceduresp. 4
1.3 Multivariate Control Proceduresp. 5
1.4 Characteristics of a Multivariate Control Procedurep. 9
1.5 Summaryp. 11
2 Basic Concepts about the T[superscript 2] Statisticp. 13
2.1 Introductionp. 13
2.2 Statistical Distancep. 13
2.3 T[superscript 2] and Multivariate Normalityp. 17
2.4 Student t versus Hotelling's T[superscript 2]p. 20
2.5 Distributional Properties of the T[superscript 2]p. 22
2.6 Alternative Covariance Estimatorsp. 26
2.7 Summaryp. 28
2.8 Appendix: Matrix Algebra Reviewp. 28
2.8.1 Vector and Matrix Notationp. 29
2.8.2 Data Matrixp. 29
2.8.3 The Inverse Matrixp. 30
2.8.4 Symmetric Matrixp. 30
2.8.5 Quadratic Formp. 31
2.8.6 Wishart Distributionp. 32
3 Checking Assumptions for Using a T[superscript 2] Statisticp. 33
3.1 Introductionp. 33
3.2 Assessing the Distribution of the T[superscript 2]p. 33
3.3 The T[superscript 2] and Nonnormal Distributionsp. 37
3.4 The Sampling Distribution of the T[superscript 2] Statisticp. 37
3.5 Validation of the T[superscript 2] Distributionp. 41
3.6 Transforming Observations to Normalityp. 47
3.7 Distribution-Free Proceduresp. 48
3.8 Choice of Sample Sizep. 49
3.9 Discrete Variablesp. 50
3.10 Summaryp. 50
3.11 Appendix: Confidence Intervals for UCLp. 51
4 Construction of Historical Data Setp. 53
4.1 Introductionp. 54
4.2 Planningp. 55
4.3 Preliminary Datap. 57
4.4 Data Collection Proceduresp. 61
4.5 Missing Datap. 62
4.6 Functional Form of Variablesp. 64
4.7 Detecting Collinearitiesp. 65
4.8 Detecting Autocorrelationp. 68
4.9 Example of Autocorrelation Detection Techniquesp. 72
4.10 Summaryp. 78
4.11 Appendixp. 78
4.11.1 Eigenvalues and Eigenvectorsp. 78
4.11.2 Principal Component Analysisp. 79
5 Charting the T[superscript 2] Statistic in Phase Ip. 81
5.1 Introductionp. 81
5.2 The Outlier Problemp. 81
5.3 Univariate Outlier Detectionp. 82
5.4 Multivariate Outlier Detectionp. 85
5.5 Purging Outliers: Unknown Parameter Casep. 86
5.5.1 Temperature Examplep. 86
5.5.2 Transformer Examplep. 89
5.6 Purging Outliers: Known Parameter Casep. 91
5.7 Unknown T[superscript 2] Distributionp. 92
5.8 Summaryp. 96
6 Charting the T[superscript 2] Statistic in Phase IIp. 97
6.1 Introductionp. 98
6.2 Choice of False Alarm Ratep. 98
6.3 T[superscript 2] Charts with Unknown Parametersp. 100
6.4 T[superscript 2] Charts with Known Parametersp. 105
6.5 T[superscript 2] Charts with Subgroup Meansp. 106
6.6 Interpretive Features of T[superscript 2] Chartingp. 108
6.7 Average Run Length (Optional)p. 111
6.8 Plotting in Principal Component Space (Optional)p. 115
6.9 Summaryp. 118
7 Interpretation of T[superscript 2] Signals for Two Variablesp. 119
7.1 Introductionp. 119
7.2 Orthogonal Decompositionsp. 120
7.3 The MYT Decompositionp. 125
7.4 Interpretation of a Signal on a T[superscript 2] Componentp. 127
7.5 Regression Perspectivep. 129
7.6 Distribution of the T[superscript 2] Componentsp. 131
7.7 Data Examplep. 135
7.8 Conditional Probability Functions (Optional)p. 140
7.9 Summaryp. 142
7.10 Appendix: Principal Component Form of T[superscript 2]p. 143
8 Interpretation of T[superscript 2] Signals for the General Casep. 147
8.1 Introductionp. 147
8.2 The MYT Decompositionp. 147
8.3 Computing the Decomposition Termsp. 149
8.4 Properties of the MYT Decompositionp. 152
8.5 Locating Signaling Variablesp. 155
8.6 Interpretation of a Signal on a T[superscript 2] Componentp. 157
8.7 Regression Perspectivep. 162
8.8 Computational Scheme (Optional)p. 163
8.9 Case Studyp. 165
8.10 Summaryp. 169
9 Improving the Sensitivity of the T[superscript 2] Statisticp. 171
9.1 Introductionp. 172
9.2 Alternative Forms of Conditional Termsp. 172
9.3 Improving Sensitivity to Abrupt Process Changesp. 174
9.4 Case Study: Steam Turbinep. 175
9.4.1 The Control Procedurep. 175
9.4.2 Historical Data Setp. 176
9.5 Model Creation Using Expert Knowledgep. 180
9.6 Model Creation Using Data Explorationp. 183
9.7 Improving Sensitivity to Gradual Process Shiftsp. 188
9.8 Summaryp. 191
10 Autocorrelation in T[superscript 2] Control Chartsp. 193
10.1 Introductionp. 193
10.2 Autocorrelation Patterns in T[superscript 2] Chartsp. 194
10.3 Control Procedure for Uniform Decayp. 199
10.4 Example of a Uniform Decay Processp. 201
10.4.1 Detection of Autocorrelationp. 202
10.4.2 Autoregressive Functionsp. 202
10.4.3 Estimatesp. 207
10.4.4 Examination of New Observationsp. 209
10.5 Control Procedure for Stage Decay Processesp. 211
10.6 Summaryp. 212
11 The T[superscript 2] Statistic and Batch Processesp. 213
11.1 Introductionp. 213
11.2 Types of Batch Processesp. 213
11.3 Estimation in Batch Processesp. 217
11.4 Outlier Removal for Category 1 Batch Processesp. 219
11.5 Example: Category 1 Batch Processp. 221
11.6 Outlier Removal for Category 2 Batch Processesp. 226
11.7 Example: Category 2 Batch Processp. 226
11.8 Phase II Operation with Batch Processesp. 230
11.9 Example of Phase II Operationp. 232
11.10 Summaryp. 234
Appendix Distribution Tablesp. 237
Bibliographyp. 253
Indexp. 259
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