6.
Process or Product Monitoring and Control
6.5. Tutorials 6.5.4. Elements of Multivariate Analysis


Continuation of example started on the previous page  STEP 6. Plot the T^{ 2} 's against the sample numbers and include the UCL.  
Mean and dispersion T^{ 2} control charts 
The following figure displays the resulting multivariate control charts.  
Interpretation of control charts 
Inspection of this figure suggests an outofcontrol conditions at
sample numbers 1, 2, 9, 10, and 11 since these points exceed the
Tsquare for means UCL of 14.52. Fortunately, the process was
apparently back in control after the periods 912.
The problem may be caused by one or more univariates, and it could be easier to remedy than when the covariance plays a role in the creation of the undesired situation. To study the cause or causes of the problem one should also contemplate the individual univariate control charts. 