[R] ANOVA between linear models.

From: Richard Martin <radiosity_at_gmail.com>
Date: Thu, 15 May 2008 15:27:03 +0100


Hi All,

I'm accustomed to performing an ANOVA to aid in choosing between linear models (for example y~x or y~x+x^2), however with different models I can't seem to do it. I'm trying to fit an exponential model of the form ye^(bt).

Below is a code snippet that highlights what I'm trying to do

s = rnorm(100, sd = 1, mean=10)
s = s + seq(0.1,10,0.1)
x = 1:length(s)
model.lin = lm(s ~ x)

model.poly = lm(s ~x + I(x^2))
model.exp = lm(log(s) ~ x)

anova(model.lin, model.poly)
#gives the correct outcome

anova(model.lin, model.exp)
#doesn't.

This fails because of the transformation of the response variable. Can anyone give any advice as to how I should proceed - is there a different test to use in this instance, or some way of reversing the transform after the model has been fitted?

Any help greatly appreciated!!

Richard

-- 
Contendere, Explorare, Invenire, et non Cedere

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Received on Thu 15 May 2008 - 19:24:59 GMT

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