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Re: st: Repeated measures


From   David Airey <david.airey@vanderbilt.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Repeated measures
Date   Sat, 14 Mar 2009 11:33:05 -0500

.

I think measurements nested in wire is the residual in the model

anova force wiretype / wireno|wiretype /

-Dave


On Mar 14, 2009, at 11:26 AM, TA Stat wrote:

I think it is measurements nested in specimen nested in wiretype.
Your main objective is to identify whether variation among wiretype is
significant or not.  Right?

Pete

On Sat, Mar 14, 2009 at 11:12 PM, David Airey
<david.airey@vanderbilt.edu> wrote:
.

I was confused by your data layout.

Your data are really just 3 columns wide:

WireType WireNo Force

where wiretype and wireno are replicated 5 times,

So

anova force wiretype / wireno|wiretype /

is fine, or the equivalent xtmixed...

-Dave

On Mar 14, 2009, at 3:16 AM, Nikolaos Pandis wrote:

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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