[R] R² for non-linear model

[Anna Gretschel]

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<ana-lee at web.de>  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
>>
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>
>
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