Thanks Marta. I am sorry I posted on personal message. I am using the list serve for very first time so was not aware of whether to reply your email or listserv. Thanks again for make me informed.

Manmit

-----Original Message-----

From: SPSSX(r) Discussion [mailto:

[hidden email]] On Behalf Of Marta García-Granero

Sent: Wednesday, July 26, 2006 2:23 PM

To:

[hidden email]
Subject: Re: pair t test for multiple variables

Hi Manmit

I'd rather follow this exchange of messages here, if you don't mind...

MS> Thanks Marta for the solution. I had written long syntax and

MS> it did not work. Your syntax, short and sweet works perfectly

MS> alright.

One item I forgot to mention in my previous message is the problem of

hight type I error. You're running 153 t-tests, the chance that at

least one is significant by chance is really above 0.05 (i feel lazy

right now, that's why I'm not computing it, but I know it will be over

99%: 1-(0.95^153)). An overall test (like a RM ANOVA or Friedman) can

be useful to check if there at least one pair of variables that differ

signifficantly.

MS> Re: RM GLM, you raised very important point. As per my

MS> understanding, we need to classify the dependent variable and

MS> factors. In my given problem, I cannot classify any message as

MS> dependent. Usually, when I have data in column I use pair-t test

MS> and using indepdent t-test will not generate significance

MS> different. E.g. if the data is in the following manner:

MS> Begin data

MS> Id Drug1 Drug2 Drug3 Drug4

MS> 1 7 7 7 7

(message followed...)

Sorry, but I don't quite follow your reasoning. You can, and you

should use a RM ANOVA before attempting all those paired t-tests (if

it is not significant, then you needn't perform all those pairwise

comparisons):

* Simulated data (according to your layout) *.

INPUT PROGRAM.

- VECTOR m(18).

- LOOP #I = 1 TO 20.

- LOOP #J = 1 TO 18.

- COMPUTE m(#J) = 1+TRUNC(UNIFORM(7)).

- END LOOP.

- END CASE.

- END LOOP.

- END FILE.

END INPUT PROGRAM.

FORMAT m1 TO m18 (F4).

EXE.

GLM m1 TO m18

/WSFACTOR = m 18 Simple

/EMMEANS = TABLES(m)

/WSDESIGN = m .

Concerning the second point I mentioned: your data are not truly

quantitative, but ordinal. You could try Friedman test

NPAR TESTS

/FRIEDMAN = m1 TO m18.

--

Regards,

Dr. Marta García-Granero,PhD mailto:

[hidden email]
Statistician

--- "It is unwise to use a statistical procedure whose use one does

not understand. SPSS syntax guide cannot supply this knowledge (nor

this list), and it is certainly no substitute for the basic

understanding of statistics and statistical thinking that is essential

for the wise choice of methods and the correct interpretation of their

results".

(Adapted from WinPepi manual - I'm sure Joe Abrahmson will not mind)