On a T2 chart, individual points are composite values that represent multiple variables. Because of this, you may have difficulty interpreting out-of-control points and determining how much any one variable contributes to the combined point value. The case may be that all of the variables contributed to make the point out of control, or perhaps only one extreme variable skewed the composite value.
To investigate whether a specific variable contributes to an out-of-control plotted point, Minitab finds each variable's contribution by decomposing the T2 statistic. Minitab performs decomposition only when two or more observations exist in a historical stage.
You can choose to store decomposed T2 values. Minitab will then print the individual contribution of each variable for all out-of-control points.