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RE: st: finding a peak in an asymmetric curve


From   "Maarten Buis" <M.Buis@fsw.vu.nl>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: finding a peak in an asymmetric curve
Date   Tue, 11 Apr 2006 12:30:20 +0200

Ah, Ronán's interpretation of your question makes a lot more sense.

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology 
Vrije Universiteit Amsterdam 
Boelelaan 1081 
1081 HV Amsterdam 
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z214 

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Ronán Conroy
Sent: dinsdag 11 april 2006 12:24
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: finding a peak in an asymmetric curve

On 11 Aib 2006, at 09:17, Yoshiro Nagao wrote:

> Are there any statistical method
> to find the value of x for the peak,
> and show its "significance"?


Check Stata's routines for analysis of pharmacokinetic data (pretend 
your nutrient values are time and you'll fool it).

. pkexamine nutrient longevity

     Warning: the point (0, 0) is not in your data.  It will be added.

                                           Maximum concentration =  
362.5851
                                   Time of maximum concentration 
=       .02
                                 Time of last observation (Tmax) =   .
049458
                                                Elimination rate =   
15.2374
                                                       Half life =    
0.0455

     Area under the curve
     
-----------------------------------------------------------------------
                     |    AUC [0, inf.)    | AUC [0, inf.) |  AUC [0, 
inf.)
      AUC [0, Tmax]  | Linear of log conc. |   Linear fit  | 
Exponential fit
     ----------------+---------------------+---------------
+----------------
          14.64      |         31.413      |     22.994    |      31.413
     
-----------------------------------------------------------------------
     Fit based on last 3 points.


You may also look at -fracpoly- which fits fractional polynomials to 
your data.

I'm not sure what the "significance" of a peak is, and I notice that 
you have rather shyly surrounded it with quotes. What exactly do you 
want to find out about the peak.

=========
Ronán Conroy
rconroy@rcsi.ie
+353 (0) 1 402 2431
+353 (0) 87 799 97 95
www.flickr.com/photos/ronanconroy




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