[R] R Square Help (this debate again, i know!)

[surreyj]

Hello everyone, 

I have been using R to do some behavioural economic analysis for my masters
thesis, specifically fitting demand curves using nls.  

E.g.

Formula: y ~ c + b * x - a * exp(x)

Parameters:
   Estimate Std. Error t value Pr(>|t|)    
c -0.445097   0.080823  -5.507 0.005304 ** 
b -0.777105   0.059528 -13.054 0.000199 ***
a  0.011908   0.003886   3.064 0.037495 *  
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

Residual standard error: 0.1046 on 4 degrees of freedom

Number of iterations to convergence: 1 
Achieved convergence tolerance: 1.119e-06 
  (1 observation deleted due to missingness)

Now all the other demand literature reports the %/proportion of variance
accounted for (or R squared) as well as the parameter values and standard
error.

>From reading these forums I can see that R squared isn't a feature in NLS
with reasoning backing this up.

I had a chat to a supervisor and he suggested I post to here and see if
someone can give me a reference/references backing up why I shouldn't use
r-squared.  However he also said that it is used throughout all of the other
demand literature and it would appear odd to not have it in my thesis.  
My second supervisor agrees it needs to be included in the analysis. 

Can someone please advise me how to do this in R?  I suppose I could always
use excel or something but I would rather make use of the code I already
have and get it looping through quickly.  (The R-squared is the last thing
that is holding me up for finishing my results section).

Any advice would be greatly appreciated.

Regards

Surrey :)



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