Gabor,
Looking at your 2nd response, your suggestion is similar to that of
Derek Ogle. It was my misinterpretation from your first response that
elicited my original rebuttal. I apologize.
Thanks,
Tony
On 2/9/2011 2:47 PM, Gabor Grothendieck wrote:
On Wed, Feb 9, 2011 at 1:02 PM, Anthony Lawrence Nguy-Robertson
<anthony.robert...@huskers.unl.edu> wrote:
Thank you R-forum for you generous help.
Gabor Grothendieck, I am not sure if anova in the form that you suggested is
the most appropriate (This is probably more of a statistics related, rather
than R related at this point). The way I understand anova is that you are
testing the variance between the models. I know that the variance in the
'corn' models is greater than 'soybean' due to a biological reason. I don't
think this approach is correct in my case since the anova analysis is
comparing variance between different data sets.
Yes, you do an F test between the models using anova.nls except the
models I specified in my response are not the models that you used and
I think you are misinterpreting my answer even though I did explicitly
point out that the models I was referring to were not the models in
your post. The models you used can't be compared this way since they
each refer to a different data set. I corrected the approach in your
question by using nested models which both refer to the same combined
data set.
"Just to be clear the two models would each include both groups -- one
model would assume the parameters are the same for the two groups so
it would have 3 parameters and the other model would allow them to be
different (up to 6 parameters depending on how many parameters you
wish to allow to be different between the two groups) -- these are not
the models shown above."
--
Anthony L. Nguy-Robertson
Doctoral Student
University of Nebraska-Lincoln
School of Natural Resources
Center for Advanced Land Management Information Technologies (CALMIT)
223 Hardin Hall
3310 Holdrege Street
Lincoln, NE 68583
Office: 402-472-2565
Fax: 402-472-2946
Email: anguy-robert...@unlnotes.unl.edu
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