[R] cubic spline smoothers with heterogeneous variances

Bill Shipley Bill.Shipley at Usherbrooke.ca
Tue Oct 22 23:49:34 CEST 2002

Hello. I have data (plant weights over time) that are non-linear and in 
which the variance increases over time.  I have to estimate the first 
derivatives of plant weight given time (i.e. growth rate) and their se, 
using a regression smoother, and I have been considering cubic spline 
smoothers.  However, I do not know if this can be done given that the error 
variance would increase over time.  Does anyone know what the effect of a 
non-constant error variance has on the estimates of the 1st derivative and 
its se?

Bill Shipley
Departement de biologie
Universite de Sherbrooke
Sherbrooke (Quebec) CANADA J1K 2R9
Bill.Shipley at USherbrooke.ca

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