I've recently reread the section about t-test, comparing means in two independent subgroups and know the formula, how to compute the t-coefficient.
Now I'm facing the question, whether the difference in my subgroups is the same as the difference, given by some other, larger study. In the t-formula it is easy to insert the theoretical difference of means - just put in the numerator of
$$ T = { \bar x_1 - \bar x_2 \over \cdots} $$ the theoretical difference
$$ T = { (\bar x_1 - \bar x_2) - (\mu_1-\mu_2) \over \cdots} $$
(if I recall the formula correctly).
But I don't find an option in SPSS to insert that theoretical difference in the calculation.
Q: Is there any procedure to get that comparision or at least some workaround in SPSS?
Rereading the section in "Bortz, Statistik für Sozialwissenschaftler" it seems, that it could be a workaround, to simply "correct" for the theoretical difference. For instance if I have the theoretical difference of means being 2.5 (years of age of the groups of male and female students, male being 2.5 years older than the female in the larger study) then I could add 2.5 to the means of the female students (if (sex=1)age=age+2.5 .
) and test for difference=0 now. Is that a meaningful option?