[R] Strange R squared, possible error

[Bert Gunter]

On Wed, Mar 16, 2011 at 4:00 PM, derek <jan.kacaba at gmail.com> wrote:
> 1) In my very humble opinion R^2 can't be negative, at least for data for
> which it sound to use linear model.

!!! Your opinion, humble or not, counts for nothing. Thomas stated a
mathematical fact. I suggest you make an effort to understand what he
said.

-- Bert


> Or the data would have to be utterly wrong to fit them with linear model.
>
> 2) I don't want to fit data with linear model of zero intercept.
> 3) I dont know if I understand correctly. Im 100% sure the model for my data
> should have zero intercept.
> The only coordinate which Im 100% sure is correct. If I had measured quality
> Y of a same sample X0 number of times I would get E(Y(X0))=0.
>
> Basically what I need to compute is R^2=1- (sum(residue^2))/(sum(Y[i])) both
> for model with and without intercept. I don't want to consider null model
> (model with zero intercept) at all.
>
> I don't know why to use y* in  R^2 = 1 - Sum(R[i]^2) / Sum((y[i]- y*)^2)
>
> --
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