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