[R] cubic spline smoothers with heterogeneous variances

[Bill Shipley]

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
http://callisto.si.usherb.ca:8080/bshipley/

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