Plot a polynomial regression

Date: Mon, 02 Nov 2009 15:42:53 -0800
From: Emily Benson <erbenson1 at gmail.com>
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Hi,
For these data, my independent variable is river discharge (Discharge) and
my dependent variable is an estimate of gross primary production (GPP). I
have fitted a polynomial regression to my data using the following command:

model<-lm(GPP ~ poly(Discharge, 2), data=nighttimeds1.dat)

I can produce a scatterplot of the data using the following commands:

# Make a plot with Discharge on the x-axis and GPP on the y-axis;
library(lattice)
xyplot((GPP)~(Discharge), groups=Site, data=nighttimeds1.dat,

+ col=c("red","blue","green","yellow"), type="p")
What I would like to do is include the polynomial regression curve on the
scatterplot of the data, but I cannot figure out how to do this.
Can anyone help me?
Thank you,
Emily

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