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st: Correlation of repeated baseline measures in sampsi


From   Helen CONNOLLY <[email protected]>
To   [email protected]
Subject   st: Correlation of repeated baseline measures in sampsi
Date   Tue, 22 Mar 2011 22:21:57 +0100

Hello,

I'm using the sampsi command to calculate sample size for a two-sample
study with 12 monthly baseline measurements and 12 monthly follow-up
measurements.  I have data from a previous study and can calculate mean
and standard deviations for both samples.

My question is, how do I calculate correlation of baseline measurements
(r0), correlation of follow-up measurements (r1), and correlation
between baseline and follow-up measurements (r01)?  These require a
single measure (not a covariance matrix).  In all the references I have
seen, there are statements like "correlation of baseline measurements
calculated from previous study", but I see no reference as to how this
is done.  Can someone please help?

Thank you,
Helen Connolly

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