Pascale,

If you do want an nls fit with the associated error structure
assumptions, check ?SSlogis.

 fm <- nls(y ~ SSlogis(x, Asy, xmid, scal))
 summary(fm)
 xx <- seq(123, 248, length = 101)
 yy <- predict(fm, list(x = xx))
 plot(x, y)
 lines(xx, yy)

 -Peter Ehlers

Gabor Grothendieck wrote:
A simple y vs log(x) fit seems to work pretty well here:

fit <- lm(y ~ log(x))
summary(fit)

plot(y ~ log(x))
abline(fit)

On Fri, Dec 4, 2009 at 9:06 AM, Pascale Weber <pascale.we...@wsl.ch> wrote:

Hi to all

This is the first time I am quoting a question and I hope, my question is
not too basic...

For the following data, I wish to draw a fitted curve.

x <- c(123,129,141,144,144,145,149,150,158,159,163,174,183,187,242,248)

y <-
c(14.42,26.96,31.3,19.95,36.36,15.4,24.76,35.39,28.07,40.97,26.23,42.83,46.53,14.79,49.18,48.08)

If I plot the data, it looks somehow that a logistic function would render
good results.

My questions are:

How do I use
 nls and/or SSlogis (or other)
to fit the curve?

How can I see the summary statistics of the fit?

How do I finally draw the line to my x,y (untransformed data) plot?

Any help would be highly appreciated.

Thank you and cheers

Pascale

--
____________________________________..___________________

Dr. Pascale Weber
Swiss Federal Research Institute WSL
Zuercherstrasse 111
CH-8903 Birmensdorf
Switzerland

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