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st: Repeated measures


From   Nikolaos Pandis <npandis@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Repeated measures
Date   Sat, 14 Mar 2009 01:16:03 -0700 (PDT)

Dear Statalisters,

I have the following dataset (except I have it in long format-one measurement per row) :

WireType	WireNo	Trial		Force

A	A1	1,2,3,4,5	      5 measurements-1 per trial
A	A2	1,2,3,4,5	      5 measurements-1 per trial
A	A3	1,2,3,4,5	      5 measurements-1 per trial
A 	A4	1,2,3,4,5	      5 measurements-1 per trial
A	A5	1,2,3,4,5	      5 measurements-1 per trial

B	B1	1,2,3,4,5	      5 measurements-1 per trial
B	B2	1,2,3,4,5	      5 measurements-1 per trial
B	B3	1,2,3,4,5	      5 measurements-1 per trial
B	B4	1,2,3,4,5	      5 measurements-1 per trial
B	B5	1,2,3,4,5	      5 measurements-1 per trial


C	C1	1,2,3,4,5	      5 measurements-1 per trial
C	C2	1,2,3,4,5	      5 measurements-1 per trial
C	C3	1,2,3,4,5	      5 measurements-1 per trial
C	C4	1,2,3,4,5	      5 measurements-1 per trial
C	C5	1,2,3,4,5	      5 measurements-1 per trial

D	D1	1,2,3,4,5	      5 measurements-1 per trial
D	D2	1,2,3,4,5	      5 measurements-1 per trial
D	D3	1,2,3,4,5	      5 measurements-1 per trial
D	D4	1,2,3,4,5	      5 measurements-1 per trial
D	D5	1,2,3,4,5	      5 measurements-1 per trial

I am testing the forces generated by 4 different wiretypes to see if there are significant differences. 
For each wiretype (categorical A B C D) I am using 5 specimens (A1-5,..D1-5) and for each specimen I am repeating the measurement 5 times. 
The outcome is force and it is a continuous variable.

This looks like a repeated measures with each trial nested in the WireNo and the WireNo nested inside WireType?

I was trying to use the xtgee command but I was not sure how to construct it:
xi:xtreg force i.xxxxx i.yyyyyy, i(zzzzz) ?

Any help would be appreciated.

Thank you very much,

Nikolaos



      
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