CTABLES always considers all the columns in the table when doing the test. You can exclude columns you don't want to be considered by using the Categories and Totals subdialog or the CATEGORIES subcommand.
You can also control the variance calculation via the COMPARETEST subcommand:
MEANSVARIANCE
Computation of variance for means test. This keyword is ignored unless TYPE=MEAN.
ALLCATS
For ordinary categorical variables, variance is estimated from all categories.
TESTEDCATS
For ordinary categorical variables, variance is estimated from the categories that are compared.
The variance for the means test is always based on the categories that are compared for multiple response tests.
You can find details on the calculations in the Algorithms manual.
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