Example of Generalized Variance Chart

A quality engineer wants to monitor the variability in the tear strength, glossiness, and opacity of plastic sheets that her company manufactures. She measures four sheets a day for 10 days. Previous analyses have found that these variables are correlated.

The engineer creates a Generalized Variance chart to simultaneously monitor the variation of tear strength, glossiness, and opacity of the plastic sheets over 10 days.

  1. Open the sample data, PlasticSheets.MTW.
  2. Choose Stat > Control Charts > Multivariate Charts > Generalized Variance.
  3. In Variables, enter Tear Gloss Opacity.
  4. In Subgroup sizes, enter Subgroup.
  5. Click OK.

Interpret the results

The joint variation of the tear strength, glossiness, and opacity is above the upper control limit at point 6. The engineer should investigate why the variation is not in control and correct the issues.

Generalized Variance Chart of Tear, ..., Opacity

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