# Fitting logistic curve to growth data

3 messages
Open this post in threaded view
|
Report Content as Inappropriate

## 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
Open this post in threaded view
|
Report Content as Inappropriate

## Re: Fitting logistic curve to growth data

 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:[hidden email]] On Behalf Of DP_Sydney Sent: Wednesday, December 28, 2011 6:07 AM To: [hidden email] 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 -- View this message in context: http://spssx-discussion.1045642.n5.nabble.com/Fitting-logistic-curve-to-growth-data-tp5105041p5105041.html Sent from the SPSSX Discussion mailing list archive at Nabble.com. ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD