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Re: st: finding a peak in an asymmetric curve


From   Ronán Conroy <rconroy@rcsi.ie>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: finding a peak in an asymmetric curve
Date   Tue, 11 Apr 2006 11:23:59 +0100

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
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