[R] logistric regression: model revision
David Winsemius
dwinsemius at comcast.net
Mon Nov 7 17:05:46 CET 2011
On Nov 7, 2011, at 10:58 AM, Sally Ann Sims wrote:
> Hello,
>
> I am working on fitting a logistic regression model to my dataset.
> I removed the squared term in the second version of the model, but
> my model output is exactly the same.
>
> Model version 1: GRP_GLM<-glm(HB_NHB~elev
> +costdis1^2,data=glm_1,family=binomial(link=logit))
> summary(GRP_GLM)
>
>
> Model version 2: QM_1<-glm(HB_NHB~elev
> +costdis1,data=glm_2,family=binomial(link=logit))
> summary(QM_1)
>
>
> The call in version 2 has changed:
> Call:
> glm(formula = HB_NHB ~ elev + costdis1, family = binomial(link =
> logit),
> data = glm_2)
> But Iâ€™m getting the exact same results as I did in the model where
> costdis1 is squared.
Are you sure that you got output that correctly modeled the
costdis1^2? I would ahve guessed that you would have needed to use :
GRP_GLM<-glm(HB_NHB~elev+I(costdis1^2), data=glm_1,
family=binomial(link=logit))
?I
The "^" in model formulas is for composing interactions.
?formula
>
> Any ideas what I might do to correct this? Thank you.
>
> Sally
> [[alternative HTML version deleted]]
And please post in plain text.
--
David Winsemius, MD
West Hartford, CT
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