08-03-2017 06:33 PM
I have a quick question about testing the assumption for paired t-tests that " The distribution of the differences in the dependent variable between the two related groups should be approximately normally distributed".
Say I have two groups one and two. The way I am supposed to do this is to create a new variable "diff=one-two"
Proc Univariate data=x normal;
qqplot / Normal (mu=est sigma=est);
Is this correct?
Or do i use this instead to test normality?
var one two;
I interpreted it as I am supposed to test the normality of the differences between groups not each group.
08-03-2017 07:08 PM
Actually I'd probably use Proc Ttest. With ODS Graphics on the defaults will create some plots related to the distributions of differences. If I didn't see any problems then we're done.
Use the VAR Diff version. If you use two variables you will get separate results for each variable in Univariate.
08-05-2017 07:39 AM
I think both are equality. If both one and two are normal distribution, then dif=one-two must be normal distribution. because dif is linear combination of normal distribution.