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RE: st: finding a peak in an asymmetric curve


From   "David Harrison" <david.harrison@icnarc.org>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: finding a peak in an asymmetric curve
Date   Tue, 11 Apr 2006 12:53:48 +0100

Yes, why didn't I think of that form...?

Anyway, one other useful point to note. You can get a confidence
interval on the position of the maximum from the -nl- function (having
worked out how to express it as a function of the parameters) by using
-nlcom-:

nlcom ln(_b[/delta] / _b[/beta]) / (_b[/beta] - _b[/delta])

David

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Joseph
Coveney
Sent: 11 April 2006 12:26
To: Statalist
Subject: Re: st: finding a peak in an asymmetric curve

The old pharmacokinetics standby (below) seems to do okay for your
example

nl (longevity = {alpha}*exp({beta}*nutrient) + ///
  {gamma}*exp({delta}*nutrient)), nolog

display in smcl as result 1 / (-_b[/delta] + _b[/beta]) * ///
   ln(_b[/delta] / _b[/beta])

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