Why do I get a message about empty cells when I try to create a multi-vari chart?

If you do not have observations for enough factor level combinations, you cannot create a multi-vari chart.

To create a multi-vari chart, you must include observations for at least 60% of the possible combinations of factor levels. Each possible combination of factor levels is a cell.

Suppose you are studying two factors, A and B. Factor A has three levels and Factor B has two levels. There are six possible combinations of factor levels (cells) in this design. If data are not included for one of these combinations, it creates an empty cell (*).

Three of the six factor level combinations, do not have observations. Thus, Minitab cannot create a multi-vari chart.
C1 C2 C3
A B Observations
A 1 *
B 1 20
C 1 *
A 2 22
B 2 *
C 2 21
A 1 *
B 1 23
C 1 *
... ... ...