[R] Fitting power laws to size distribution data

[Gough Lauren]

Hi,

I have several datasets recording the size of individuals shrubs.  I
would like to test various distribution functions to see which fits my
data most closely.  So far I have used the fitdistr tool in the MASS
package to get the parameter estimates for the best-fit lognormal,
exponential and two-paramater Weibull functions.  I have compared the
fit of these functions using AIC.

I would also like to fit a power function of the form f(D) = kD(^-r)
(this is the form most of the relevant literature uses) obtaining
estimates of the exponent (r).  However, the power function does not
appear to be supported by fitdistr.

I have searched the forums and the internet and found a few ways of
fitting power functions, but having run them they are giving me wildly
different exponent estimates.  

Can anyone suggest a relaible way of fitting power functions?  

Many thanks

Lauren


This message has been checked for viruses but the contents of an attachment
may still contain software viruses, which could damage your computer system:
you are advised to perform your own checks. Email communications with the
University of Nottingham may be monitored as permitted by UK legislation.