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Re: st: R: ANOVA repeated measures


From   "JVerkuilen (Gmail)" <jvverkuilen@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: R: ANOVA repeated measures
Date   Tue, 6 Nov 2012 10:16:12 -0500

Yes there's a clear risk of non-normality in meausres such as this. If
the measure has a multiplicative structure (as bacterial growth might)
then logging first would help.

On Tue, Nov 6, 2012 at 9:41 AM, Carlo Lazzaro
<carlo.lazzaro@tiscalinet.it> wrote:
> 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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-- 
JVVerkuilen, PhD
jvverkuilen@gmail.com

"Thus the typical citizen drops down to a lower level of mental
performance as soon as he enters the political field. He argues and
analyzes in a way which he would readily recognize as infantile within
the sphere of his real interests. He becomes a primitive again. His
thinking becomes associative and affective."  ---Joseph A. Schumpeter,
Capitalism, Socialism and Democracy, 1950, p. 262.

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