09-02-2011 04:54 AM
Dear SAS users
I'd like to study growth curves. I have weight data points for several individuals (several data points per individual - at different ages) and I'd like to retrieve from the growth curve (which is not linear) parameters such as: growth velocity, age at which a plateus is attained etc... I'll then compare these different parameters among the studied individuals.
Gompertz curves could be appropriate (with the NLMIXED procedure) but I really had troubles designing the adequate procedure. Could you please help me here?
Thanks a lot in advance!
09-02-2011 05:05 AM
This is a classic application of quantile regresion. There are several examples of doing this in the doc for the QUANTREG procedure. For a parametric model, see http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_qreg_sect006...
For a nonparametric spline model (which uses the new EFFECT statement), see http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_qreg_sect034...