From: Schatzi <adele_thompson_at_cargill.com>

Date: Wed, 27 Apr 2011 06:28:45 -0700 (PDT)

Date: Wed, 27 Apr 2011 06:28:45 -0700 (PDT)

Here is more information on the equation. It is a growth function:

Growth = a + b*(1-exp(-k*time))

where a, b and k are parameters. I wanted to test the difference in total growth between treatments and the parameters a + b represent total growth. Thus, I figured that I could add the parameters and the SE to test the treatment differences. I also need the rate constant k and the initial values a and their treatment differences. I found the equation I posted on this website: http://sci.tech-archive.net/Archive/sci.math/2004-07/4780.html This book was referenced: Kendall & Stuart's Advanced Theory of Statistics

Thanks for all you your help.

Adele

From: ml-node+3477116-1659458804-211414_at_n4.nabble.com [mailto:ml-node+3477116-1659458804-211414_at_n4.nabble.com]
Sent: Tuesday, April 26, 2011 09:29 PM

To: Thompson, Adele - Adele_Thompson_at_cargill.com
Subject: Re: How can I extract information from list which class is nls

On Tue, Apr 26, 2011 at 2:21 PM, Schatzi <[hidden email]</user/SendEmail.jtp?type=node&node=3477116&i=0&by-user=t>> wrote:

> How do I extract the standard error of the parameter estimates?

*>
**> Also, if I would like to add two parameters together (x+y), can I use this
**> equation to calculate the new standard error?:
**> x = parameter 1
**> y = parameter 2
**> xSE = SE parameter 1
**> ySE = SE parameter 2
**>
**> NewSE=(x+y)*sqrt((xSE/x)^2+(ySE/y)^2)
*

Try taking the square roots of their variance:

> example(nls)

*> sqrt(diag(vcov(fm1DNase1)))
*

Asym xmid scal

0.07815395 0.08135321 0.03227080

*>
*

> # it gives the same result as another solution

*> # offered on this thread
**> coef(summary(fm1DNase1))[, "Std. Error"]
*

Asym xmid scal

0.07815395 0.08135321 0.03227080

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