R help - Aug 2009 - how to specify two variance effects in gls

Hello everybody,

I have a dataset where each row has number of subjects and that gives me natural
weights for the variance function. Additionally I see that variance increases
with Age, which is a regressor.
So using gls I have



weights=varFixed(~1/n)

but don't know how to include the extra effect of the regressor.
Fitted values show a quadratic curve vs. age, not sure if that helps.

Thanks everybody.
Stephen

	[[alternative HTML version deleted]]

I got the answer:

weights=varComb(varFixed(~1/n),varPower(~Age))



Bond, Stephen-2 wrote:
> 
> Hello everybody,
> 
> I have a dataset where each row has number of subjects and that gives me
> natural weights for the variance function. Additionally I see that
> variance increases with Age, which is a regressor.
> So using gls I have
> 
> 
> 
> weights=varFixed(~1/n)
> 
> but don't know how to include the extra effect of the regressor.
> Fitted values show a quadratic curve vs. age, not sure if that helps.
> 
> Thanks everybody.
> Stephen
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 
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