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st: RE: re:linear regression with robust variance estimation


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: re:linear regression with robust variance estimation
Date   Fri, 6 Feb 2009 14:28:48 -0000

I don't know how much help this would be statistically, or
scientifically, but in such cases I would always have a quick look at 

second baby - first baby 

perhaps plotted against their mean. If babies are better logged or
otherwise transformed, that's a further wrinkle. 

Nick 
n.j.cox@durham.ac.uk 

Kit Baum

Ali said
I have a small data set of 136 infants each 2 of them have the same  
mother. All mothers have a disease which I am at its effect on  
birthweight. These women were diagnosed and treated after giving birth  
for the first child. I am trying to measure the difference in mean  
birthweight between infants who were born before treatment and those  
who were born after treatment. At the same time I want to account for  
parity (3 categories 1, 2 or 3) and gestational age (4 categories).

I am using regress with robust option to account for the fact that the  
data is not independent. Is there a way to include the mothers  
personal number in the model? Or does robust take into this problem  
into account?

The model I used is x: regress birthweight i.disease i.parity  
i.gestationalage, robust


why not cluster(motherid) ? That subsumes robust and allows for error  
correlation among children of the same mother.

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