Title page for ETD etd-05022009-040726

Type of Document Master's Thesis
Author Hanson, Robert Alexander
URN etd-05022009-040726
Title The application of a single control chart for dependent variables in multivariate quality control
Degree Master of Science
Department Industrial Engineering and Operations Research
Advisory Committee
Advisor Name Title
Fabrycky, Wolter J. Committee Member
Nachlas, Joel A. Committee Member
Schmidt, J. William Committee Member
  • Quality control
Date of Defense 1990-08-05
Availability restricted

Most control charts monitor only one quality characteristic. There are, however, many manufactured products for which good quality requires meeting specifications in more than one physical characteristic. Typical practice when dealing with multiple quality characteristics is to take a separate sample for each characteristic and then create individual univariate control charts which are independently monitored. This method can result in errors due to not accounting for the effects of correlation. In order to avoid these errors, an alternate approach to multivariate quality control problems is proposed and studied here. The original problem is converted into a univariate problem by using the following transformation:

y=Σ aixi i where αi = weighting coefficient for the ith quality characteristic Xi = represents the ith quality characteristic

This transformation retains sensitivity to changes in the original quality variables. The resulting univariate quality control model takes into account the sampling error probabilities for each of several candidate hypotheses. The probabilities of correctly diagnosing process shifts when an out-of-control state occurs are calculated and tabulated as are the probabilities that the model will signal when an out-of-control state occurs.

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