Dear list users
How is it possible to visualise both a linear trend line and a quadratic trend
line on a plot
of two variables?
Here my almost working exsample.
data(Duncan)
attach(Duncan)
plot(prestige ~ income)
abline(lm(prestige ~ income), col=2, lwd=2)
Now I would like to add yet another trend line, but this time a quadratic one.
So I have two
trend lines. One linear trend line and a quadratic trend line. A trend line as
if I had taken
I(income^2) into the equation.
I know I can make two models and compare them using anova, but for pedagogical
resons I wold
like to visualise it. I know the trick from my past as an SPSS user, but I
would like to do
this in R as well. Se it in SPSS
http://www.childrens-mercy.org/stats/weblog2006/QuadraticRegression.asp
Thanks in adcance
Eric
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