http://spssx-discussion.165.s1.nabble.com/Longitudinal-comparison-partial-vs-whole-sample-tp5718123p5718140.html
If we assume that you are going to present this to a somewhat critical
audience, then you have to state some hypotheses to go along with a
rational narrative.
Do the 20 differ at time T1 from T2? That is a paired t-test. That is
the very sensible first test that you might perform if you expect changes.
For something with (I expect) large individual variations like eye tracking,
that test will have more power than a grouped test.
Do the 20 differ from 56 at T1? That is a simple grouped t-test. That is
a very sensible and necessary test to perform, if you are going to say
anything about both times.
If the 20 vs. 56 happen to differ at T1 (or differ for some definite reason),
that limits the narrative.
After describing those differences -- or, preferably, no differences -- I
suppose that you could carefully explain that you want to treat the 76
at T1 as a normative sample, and (therefore) here is what you would see
as that test.
--
Rich Ulrich
> Date: Tue, 19 Feb 2013 02:41:32 -0800
> From:
[hidden email]> Subject: Longitudinal comparison partial vs. whole sample
> To:
[hidden email]>
> Hello everybody,
>
> I have eye tracking data of a total sample (n = 76) at testing point 1 (T1)
> and of a partial sample (n = 20) at testing point 2 (T2).
>
> I want to compare the eye tracking performances of the test persons from the
> partial sample at T2 with those of the total sample at T1.
>
> That means, that the total sample should represent a norm sample and I want
> to test, whether the T2 partial sample differs from this norm.
>
> Which statistical test do I have to use (bearing in mind the longitudinal
> design) and how do I do that in SPSS?
>
> If possible: Do you have any literature references for an approach
> concerning this "problem".
>
> Best regards,
>