On Mar 20, 2011, at 3:56 PM, Anna Lee wrote:
Dear Ista!
Thank you for replying. The point you made is exactly what's the
problem: I want to predict the values at different points in space.
calP stands for the water content at each sampling point (n=90) but I
don't quite understand what R does. calP is my vector of measured data
and I thought with the predict function the programm would calculate a
value from the model function for every value of calP... ?
I do not think you are reading Ista Zahn comments carefully. She said
you needed to offer you newdata argument as a data.frame. That is the
fundamental problem.
She also pointed out that your arguments in the list didn't seem to
represent a full explorations of the data "space". If all of the
variables in the regression problem have the same value for each case,
then there is no point in adding multiple variables.
--
David.
2011/3/20 Ista Zahn <iz...@psych.rochester.edu>:
Hi Anna,
On Sun, Mar 20, 2011 at 2:54 PM, Anna Lee <ana-...@web.de> wrote:
Hey List,
I did a multiple regression and my final model looks as follows:
model9<-lm(calP ~ nsP + I(st^2) + distPr + I(distPr^2))
Now I tried to predict the values for calP from this model using the
following function:
xv<-seq(0,89,by=1)
yv<-predict(model9,list(distPr=xv,st=xv,nsP=xv))
The second argument to predict.lm is newdata, which should be a
data.frame. see ?predict.lm.
Beyond that though, I'm not sure what you are trying to accomplish.
The way you've set this up you would get predicted values for cases
like
distPr st nsp
0 0 0
1 1 1
2 2 2
. . .
89 89 89
Is that really what you want?
Best,
Ista
The predicted values are however strange. Now I do not know weather
just the model does not fit the data (actually all coefficiets are
significant and the plot(model) shows a good shape) or wether I did
something wrong with my prediction command. Does anyone have an
idea???
--
Thanks a lot, Anna
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--
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org
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David Winsemius, MD
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