[R] what characteristics of model curve do parameters denote
Dear list, I'm trying to fit a chapman-richards equation to my data, only I cannot interpret the parameters a, b and d. I know that the parameter b denotes the asymptote, but for the others I couldn't figure out. But I do need to know this in order to set my starting values. Here's the model: modPoplar<- nls(Diameter ~ d*(1-exp(-b *Age))^a ,start=list(a=20,b=0.9,d=33)) I attached the graph, too. Hoping for your answers! Best, Anna -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Telefon: 01577-7805329 E-Mail: gretschel.a...@googlemail.com __ R-help@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.
Re: [R] R² for non-linear model + comparing linear + non-linear models
Am 16.03.2011 19:29, schrieb Heiman, Thomas J.: Hi Anna, AIC and BIC are good criteria for determining degree of model fit.. Sincerely, tom Thomas Heiman, PhD Info Systems Eng, Sr The MITRE Corporation | Center for Enterprise Modernization Office: 703-983-2951 | thei...@mitre.org -Original Message- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Anna Gretschel Sent: Wednesday, March 16, 2011 2:09 PM To: Bert Gunter Cc: r-help@r-project.org Subject: Re: [R] R² for non-linear model + comparing linear + non-linear models Dear Bert, so what can I do to obtain a goodness of fit for a non-linear model if r² does not work? And here comes my next question: is it apropriate to comopare a linear and a non-linear model with anova()? Thank you so much for answering, Anna Am 16.03.2011 18:54, schrieb Bert Gunter: Is there any way that this could be made into a fortune -- perhaps by omitting the poster's identity? "yes there are threads concidering this topic but they are all about the theory not about how to get the value of r^2 for a non-linear model in R." :=) Cheers, Bert Anna: I say this because you have just been told that the "theory" tells you that you CANNOT calculate R^2 for a nonlinear model. On Wed, Mar 16, 2011 at 10:25 AM, Anna Gretschel wrote: Am 16.03.2011 18:15, schrieb David Winsemius: On Mar 16, 2011, at 12:53 PM, Anna Gretschel wrote: Dear List, how can I obtain the value of r suqared for a non-linear model? For linear models it can be found in the summary() of the model but for non-linear models I just don't know. Please help! You should do more searching. I can remember at least two threads in the last few years that discussed this issue. yes there are threads concidering this topic but they are all about the theory not about how to get the value of r^2 for a non-linear model in R. __ R-help@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. __ R-help@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. Thank you so much! Anna __ R-help@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.
Re: [R] R² for non-linear model + comparing linear + non-linear models
Dear Bert, so what can I do to obtain a goodness of fit for a non-linear model if r² does not work? And here comes my next question: is it apropriate to comopare a linear and a non-linear model with anova()? Thank you so much for answering, Anna Am 16.03.2011 18:54, schrieb Bert Gunter: Is there any way that this could be made into a fortune -- perhaps by omitting the poster's identity? "yes there are threads concidering this topic but they are all about the theory not about how to get the value of r^2 for a non-linear model in R." :=) Cheers, Bert Anna: I say this because you have just been told that the "theory" tells you that you CANNOT calculate R^2 for a nonlinear model. On Wed, Mar 16, 2011 at 10:25 AM, Anna Gretschel wrote: Am 16.03.2011 18:15, schrieb David Winsemius: On Mar 16, 2011, at 12:53 PM, Anna Gretschel wrote: Dear List, how can I obtain the value of r suqared for a non-linear model? For linear models it can be found in the summary() of the model but for non-linear models I just don't know. Please help! You should do more searching. I can remember at least two threads in the last few years that discussed this issue. yes there are threads concidering this topic but they are all about the theory not about how to get the value of r^2 for a non-linear model in R. __ R-help@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. __ R-help@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.
Re: [R] R² for non-linear model
Am 16.03.2011 18:19, schrieb Joshua Wiley: Dear Anna, What is your goal in obtaining a value for R^2 ? I believe it is not provided for a non-linear model, because it does not make much sense. It certainly will not have the same interpretation as in a linear model, and all the ways it *could* be "defined" come with their own sets of problems. A more precise definition of what you want (say you have a particular formula but do not know how to get the necessary information out of the model) may get a better answer. Best regards, Josh On Wed, Mar 16, 2011 at 9:53 AM, Anna Gretschel wrote: Dear List, how can I obtain the value of r suqared for a non-linear model? For linear models it can be found in the summary() of the model but for non-linear models I just don't know. Please help! Anna __ R-help@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. Dear Josh, I actually want to find out the goodness of fit. I have to make choises between a linear and an exponential model and I thought comparing their r squares would give me an idea of which one better explains the correlation of the data. So if r squared does not work for non-linear regression - do you have an idea how to calculate some goodness of fit? Thank you a lot for replying! Cheers, Anna __ R-help@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.
Re: [R] R² for non-linear model
Am 16.03.2011 18:15, schrieb David Winsemius: On Mar 16, 2011, at 12:53 PM, Anna Gretschel wrote: Dear List, how can I obtain the value of r suqared for a non-linear model? For linear models it can be found in the summary() of the model but for non-linear models I just don't know. Please help! You should do more searching. I can remember at least two threads in the last few years that discussed this issue. yes there are threads concidering this topic but they are all about the theory not about how to get the value of r^2 for a non-linear model in R. __ R-help@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.
[R] R² for non-linear model
Dear List, how can I obtain the value of r suqared for a non-linear model? For linear models it can be found in the summary() of the model but for non-linear models I just don't know. Please help! Anna __ R-help@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.
[R] predicting values from model function
Dear List, I have fitted a spherical function to my variogram using "variofit(...)" from GeoR. Now I would like to predict some data with the function "predict(object,...)" from package stats. Does anyone know wether this works and if it does how to do it? Thanks a lot! Anna __ R-help@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.
[R] testing power of correlation
Dear List, does anyone know how I can test the strength of a correlation? Cheers, Anna __ R-help@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.
