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st: RE: fitting a gompertz curve, not in the context of survival analysis


From   "Nick Cox" <[email protected]>
To   <[email protected]>
Subject   st: RE: fitting a gompertz curve, not in the context of survival analysis
Date   Fri, 29 May 2009 11:20:52 +0100

In addition to other comments: 

I'd be interested to know the Laird reference implied but not given
here. 

I don't know of an add-on, but no matter: you shouldn't need one. An
easy alternative should be to try -nl- with the equation specified on
the command line. 

But I'm puzzled by your intent on various levels. 

1. Growth models in biology and elsewhere that I know about presuppose a
natural time origin, i.e. a date of birth or creation. It's not obvious
to me from the rudimentary economics I know that there is an equivalent
for your problem. 

2. Otherwise put, this curve goes X(0) at time 0, but why is one data
point privileged over the others? 

Nick 
[email protected] 

Dan Waldo

I am trying to test whether government revenues as a percentage of GDP
can be fit over time with a Gompertz curve -- especially to determine
(if the fit is appropriate) the limiting value.

The help I have found comes in the form of survival analysis models,
which I have trouble reconciling to the model I am trying to fit.

Is there a Stata add-on that fits Laird's tumor-growth variant of the
Gompertz? This would be specified as:

X(t)= K exp(log(X(0)/K)exp(-at))

where X is known and K and a are estimated.


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