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st: RE: correlated data


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: correlated data
Date   Tue, 1 Sep 2009 13:28:29 +0100

You asked the same question on 23 August: 

<http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist
.0908/Author/article-1091.html> 

and received two quick but brief replies. 

Before repeating a question like this, it is usually best to think: Why
did I not get a detailed reply? Was my question not clear enough? Does
the list lack experts in this field? Should I rephrase the question? See
also 

<http://www.stata.com/support/faqs/res/statalist.html#noanswer> 

It is also best to explain why any replies you got do not help.

I don't know the answer, but I do note that list members are often more
reluctant to give strategic advice than to answer specific Stata
questions. 

Nick 
n.j.cox@durham.ac.uk 

Nikolaos Pandis

We have a set of 3-D images constructed from cat scans, and we are
measuring volumes defined by certain anatomical points on the 3-D
images.

The reconstruction/measuring technique is performed using 3 new types of
software and their results will be compared with the results of
validated/reference technique.

The same reconstructions/cat scans are used for all techniques.

The objective is to see how close (do they differ significantly?) the
volume values recorded by each technique are to the values recorded by
the reference technique.

I was thinking along the lines of regression with the volume(continuous)
variable as the dependent variable and technique as the categorical
dependent variable with 4 levels. The reference level would be the the
standard/validated method.

However, how would I account for the fact that the data is correlated
since all measurements for the 4 methods are taken from the same
reconstructions/scans?

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