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st: correlation


From   fponzano@unipmn.it
To   statalist@hsphsun2.harvard.edu
Subject   st: correlation
Date   Tue, 4 Dec 2007 10:29:19 +0100 (CET)

Dear all,
I have to check for correlation among variables. The data come from a
within - subject experiment. This is an example to illustrate how my data
are organized (I have 40 groups at the moment - distributed over 3
treatments):

id    group    x1    x2    x3
1       1         15    15    20
2       1         15    20    20
3       1         18    18    18
4       1         15    15    15
5       2         20    20    20
6       2         18    18    18
7       2         18    18    20
8       2         20    20    20

I want to check whether, for each individual (id), x1, x2 and x3 are
correlated.
My question is: is it correct to run a Spearman's correlation test (or a
Pearson's correlation test if I manage to collect more observations) even
if observations within the same group are probably not independent? What
should I do?
Thank you

F.P.

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