Computing MSPE in Minitab

The MSPE (the average of cell variances) can be obtained in a couple different ways. If you have entered all your data in a single column, you can enter another column containing a cell identifier. Suppose you had replicated an 8-run design 5 times and the data was entered in C1. From the Edit>Command Line Editor window in Minitab, you could enter (and then press Submit):

set c2
(1:8)5
end

You can then ask for descriptive statistics (by c2) to obtain the cell variances. Select Stat>Basic Statistics>Store Descriptive Statistics. Enter C1 in the Variables box, and C2 in the By Variables box. In the Statistics menu, check Variance; Minitab will automatically store the variances in a column. Assume the variances are stored in C4. Back in the Edit>Command Line Editor window, type

Average C4

to obtain the MSPE.

If you have entered the reps in 5 separate columns, you can use a row operator to obtain variances. If the reps are in columns C1-C5, select Calc>Row Statistics. Check Standard Deviation (Minitab does not have a Variance option), enter C1-C5 in the Input Variables box and C6 in the Store Result In box. In the Calculator, enter the formula: mean(c6*c6), and store the result in C7 to obtain the MSPE.