Re: [R] Strange R squared, possible error

From: derek <jan.kacaba_at_gmail.com>
Date: Thu, 17 Mar 2011 08:28:54 -0700 (PDT)

Thats exactly what I would like to do. Any idea on good text? I've consulted severel texts, but no one defined R^2 as R^2 = 1 - Sum(R[i]^2) / Sum((y[i])^2-y*)) still less why to use different formulas for similar model or why should be R^2 closer to 1 when y=a*x+0 than in general model y=a*x+b.

from manual:
r.squared R^2, the ‘fraction of variance explained by the model’, R^2 = 1 - Sum(R[i]^2) / Sum((y[i]- y*)^2), where y* is the mean of y[i] "if there is an intercept" and zero otherwise.

I don't need explaining what R^2 does nor how to interpret it, because I know what it means and how it is derived. I don't need to be told which model I should apply. So the answers from Thomas weren't helpful.

I don't claim it is wrong, otherwise wouldn't be employed, but I want to see the reason behind using two formulas.

Control questions:
1) Statement "if there is an intercept" means intercept including zero intercept?

2) If I use model y = a*x+0 which formula for R^2 is used: the one with Y* or the one without?

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