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RE: st: linear mixed models doubt in how to interpret the Coef


From   "Michael Ghebre" <m.a.ghebre@qmul.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: linear mixed models doubt in how to interpret the Coef
Date   Thu, 30 Jun 2011 17:51:30 +0100

Luisa, 

I think you have variable i.year_of_visit and you can use it as time; once
you do this check the coefficient sign (+ or -) and the p-value of the
interaction. If you have significant p-value then you can interpret your
results as follows: 

For one unit increase in Glu the outcome variable (sdnn) decreases by 3.35
units at the baseline; however, that association (negative relationship)
declined by some units over time (if you have negative interaction effect)
or increases by some values if your interaction effect is positive. 

Hope this helps 
Michael 

 

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Luisa
Soares-Miranda
Sent: 30 June 2011 17:16
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: linear mixed models doubt in how to interpret the Coef

Dear Michael ,

Thank you so ouch for your help , I have tried to include in the
command the interaction glu_std * time but a error is reported. I
literally have to include in the command glu_std*? And with that I can
say that my coefficient is higher or lower over time?
regards

Luisa


On Thu, Jun 30, 2011 at 4:31 PM, Michael Ghebre <m.a.ghebre@qmul.ac.uk>
wrote:
> Luisa,
>
> Include time and glu_std interaction (glu_std*time) in your model and that
> will tell you how that association carried out over time.
>
> Hope this helps
>
> Michael
>
> Michael A Ghebre
> Research Fellow in Medical Statistics
> Centre for Environmental and Preventive Medicine
> Wolfson Institute of Preventive Medicine
> Barts and the London School of Medicine and Dentistry
> Queen Mary University of London
> Charterhouse Square London EC1M 6BQ
> Email : m.a.ghebre@qmul.ac.uk
> Tel : 02078826267
> http://www.wolfson.qmul.ac.uk
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Luisa
> Soares-Miranda
> Sent: 30 June 2011 16:09
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: linear mixed models doubt in how to interpret the Coef
>
> Dear Maarten,
>
> Thank you for your help. But even though can I say that a longitudinal
> analyze of the associations between Glu and SDNN was cerried out?
>
> thanks
>
> Luisa
>
> On Thu, Jun 30, 2011 at 3:57 PM, Luisa Soares-Miranda
> <luisasoaresmiranda@gmail.com> wrote:
>> Dear all,
>>  I am writing you because I am performing a longitudinal mix models
>> analyses as the following
>>
>> xi: xtmixed sdnn i.year_of_visit  gender  age  smoke alcohol
>> waistcinrcunfrence_std  pa_std  tasis_std   trg_std  glu_std hdl_std
>> || id: i.year, covariance(identity)
>>
>> I have 3 years of data, my main doubt now is how can I interpret my
>> Coefficient? If my results I have that the Coef of Glu is  -3.35 and
>> the p is 0.001. Can I say that when I increase by one unit Glu sdnn
>> decreases -3.35 ms over 3 years? So Glu is associated with a decrease
>> in sdnn over time.
>> thank you so much for your help,
>> regards
>> Luisa
>>
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