Re: Multivariate comparison (Hotelling's T?)

Posted by torvon on Nov 19, 2012; 12:35am
URL: http://spssx-discussion.165.s1.nabble.com/Multivariate-comparison-Hotelling-s-T-tp5716159p5716293.html

Please excuse the late answer! For some reason my Gmail account marked your very helpful responses as spam, which had never happened before.

The point of my investigation is to how that symptoms differ from each other on various dimensions. Severity at time 1, and change from time 1 to time 2 are just two dimensions of many reported in the paper, but the ones I did not know how to investigate statistically. I absolutely want to avoid to use a sum score for "general psychopathology".

For test 1 (do symptoms at time 1 have equal severity): Rich, you are correct with your statement:
"It takes an effort to select items (and their wording) to achieve "equal difficulty" or "equal pathology" or whatever.  For one population, or several."
No one will be surprised indeed by a ridiculous Hotelling' T^2 test (I have about 150 zeros after the decimal point), but some symptoms are more than 20 times as severe as others, and I simply need a statistical test to report this fact (although it is absolutely obvious from looking at the mean scores).

For test 2, comparing whether symptoms increase differentially from each other:
"Especially if there is strong stability for scores across time, the simple
and most effective way to test for "change of profile" might be to compute
the 9 change scores and to a simple one-way repeated measures test on
that set of scores."
I don't understand what you mean. If I compute change scores, I lose repeated measures by definition because the information of 2 measurement points is merged into 1 (change). What procedure would you recommend?

If I would not use change scores, and simply want to compare s1_t0 to s1_t1, s2_t0 to t2_t1, s3_t0 to s3_t1 in a multivariate way, which procedure do I use? I found Hotelling's T in the Scale -> Reliability section as test statistic, but there is no way to specify 2 measurement points.

Thanks
T