Date:         Wed, 28 Dec 2011 09:16:45 -0500
Reply-To:     Gene Maguin <emaguin@buffalo.edu>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Gene Maguin <emaguin@buffalo.edu>
Subject:      Re: Fitting logistic curve to growth data
In-Reply-To:  <1325070409338-5105041.post@n5.nabble.com>
Content-Type: text/plain; charset="us-ascii"

Dean,

Have you looked at the curvefit procedure? It has a logistic function and,
although I haven't used it for quite a while, I recall that it yields
coefficient values.

Gene Maguin

-----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
DP_Sydney
Sent: Wednesday, December 28, 2011 6:07 AM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: Fitting logistic curve to growth data

Hi all,

 I need to fit a curve to data on mass gain, which follows a sigmoidal
pattern and is best described using a logistic equation (based on similar
published data, with which I wish to compare my data) of the form:

Y = A/(1 + e^-K(d-i))
where Y = mass
         A = asymptotic mass
         K = growth rate
         d = age (time)
         i = inflection point
        (note ^ indicates to the power)

The data I have are body mass recorded daily for several individuals
(nestling birds), which will be analysed separately.

I need to output the parameters (A, K, i) rather than just produce a curve.
I've searched the archives and Google but haven't found instructions for how
to do this (I have instructions for running this in GENSTAT but of course do
not have GENSTAT).

Any help would be great...but beware I am a drop-down menus and buttons
person when it comes to software :-)

Regards,
Dean



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