R help - Jul 2008 - Test for multiple comparisons: Nonlinear model, autocorrelation?

Dear R community, 
 
I have a nonlinear model describing average daily soil temperature. What test
should I use to compare differences in soil temperature of the two studied
vegetation types depending upon month?
 
Building linear contrasts for the developed nonlinear model does not help since
this model does not include variable “Months” (only “Days”).
 
1) Just a Student’s test is not probably an option because I would violate an
assumption of independency, since the daily soil temperature observations have
high autocorrelation. Or maybe I could average the observations for each month
and then use this test since I have observations for a few years, and it might
overcome the problem of independency?
 
2) Should I develop a second nonlinear model with months instead of days, but it
would considerably increase a number of parameters in the model...
 
Or:
3) ?
 
Thanks for your help,
Julia
_________________________________________________________________
It’s a talkathon – but it’s not just talk.

	[[alternative HTML version deleted]]

The question seems too general for me to offer specific suggestions.

What problem are you trying to solve that you think 'multiple 
comparisons' will answer?

Can you produce a similar problem that is completely self-contained 
example that eliminates complexity that may not be needed to understand 
your question (similar to the 'Auxiliary Problem' technique in "How
to
Solve It", http://en.wikipedia.org/wiki/How_to_Solve_It)? If you can, it 
may lead you to a solution. If you get such an example but still can't 
see a solution, send that example to this list (following the advice in 
the posting guide http://www.R-project.org/posting-guide.html). The 
simpler the example, the more likely someone on this list will reply 
quickly with a useful suggestion.

I know this doesn't solve your problem, but I hope it helps.
Spencer

J S wrote:
> Dear R community, 
>  
> I have a nonlinear model describing average daily soil temperature. What
test should I use to compare differences in soil temperature of the two studied
vegetation types depending upon month?
>  
> Building linear contrasts for the developed nonlinear model does not help
since this model does not include variable ?Months? (only ?Days?).
>  
> 1) Just a Student?s test is not probably an option because I would violate
an assumption of independency, since the daily soil temperature observations
have high autocorrelation. Or maybe I could average the observations for each
month and then use this test since I have observations for a few years, and it
might overcome the problem of independency?
>  
> 2) Should I develop a second nonlinear model with months instead of days,
but it would considerably increase a number of parameters in the model...
>  
> Or:
> 3) ?
>  
> Thanks for your help,
> Julia
> _________________________________________________________________
> It?s a talkathon ? but it?s not just talk.
>
> 	[[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.
>