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st: R: ANOVA repeated measures


From   "Carlo Lazzaro" <carlo.lazzaro@tiscalinet.it>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: R: ANOVA repeated measures
Date   Tue, 6 Nov 2012 15:41:37 +0100

Rune might also consider to regress the difference in bal_1 and bal_2
(diff_bal) on intervention dummy (Int).

- reg diff_bal Int - 

Otherwise, should Rune follow paired ttest approach (as previously suggested
by Jay) some concerns about the normality of bal measuremets might arise. In
this instance, Rune can opt for a bootstrap paired ttest.

Best Regards,
Carlo 
----------------------------------------------------------------------------
------------------------------------------------------------------
Da: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Rune Nielsen
Inviato: martedì 6 novembre 2012 14:56
A: statalist@hsphsun2.harvard.edu
Oggetto: st: ANOVA repeated measures

Dear statalist members,

We have done a simple pilot study where we measure the number of bacteria on
the tip of a bronchoscope two times on the same 20 subjects. Half of these
subjects have received an intervention to reduce the number of bacteria. So
in a long dataset with 40 observations  I have the following variables
Idnr - subject ID
meas - binary variable indicating first (=1) or second (=2) measurement
flush - binary variable whether the subject have received (=1) or not (=0)
the intervention
bal - measurement of bacterial load

What I would like to do, is to test whether the difference between
measurement 1 and measurement 2 is  depending on whether they have received
the intervention. I've tried various ANOVA syntaxes, but my limited
knowledge won't quite get me there. 

Probably this reveals my incompetence, but nevertheless I hope for an answer
that is understandable for a non-statisician.

Best wishes,

Rune Nielsen 

---
Rune Nielsen, MD, PhD, postdoctoral fellow
Institute of Medicine
Department of Thoracic Medicine
Haukeland University Hospital
N-5021 Bergen
Norway


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