Multivariate EWMA Chartoverview how to example data see also
Multivariate EWMA ChartStat > Control Charts > Multivariate Charts > Multivariate EWMA
The multivariate form of the EWMA control chart. You can use a MEWMA chart to simultaneously monitor two or more related process characteristics in an exponentially weighted control chart. For example, in a spray drying process, to control your product particle size, you can monitor feed temperature and chamber temperature. In the MEWMA chart, each plotted point includes weighting from all previous data, allowing you to detect small process shifts quicker than with other multivariate methods, such as the T2 control chart.
You can specify sample means, variances, and covariances for each variable or have Minitab calculate them.
For more information, see Control Charts Overview and Multivariate Control Charts Overview.
Variables: Enter at least two columns of data.
Subgroup sizes: Enter a number or a column of subscripts. If the subgroups are not equal, each control limit is not a single straight line but varies with the subgroup size. If the subgroup sizes do not vary much, you may want to force the control limits to be constant by specifying a fixed subgroup size using MEWMA Options > Estimate.
ARL: Enter the average run length. The minimum allowable ARL is 1.
Weight: Specify the weight to be used in the multivariate exponentially weighted moving average. The value must be a number between 0 and 1. By changing the weight used and the number of standard deviations for the control limits, you can construct a chart with specific properties. You can choose combinations of these two parameters by using an ARL (Average Run Length) table. See [18] for an extensive table.