[R] Logistic Regression output baseline (reference) category
Michael Artz
michaeleartz at gmail.com
Sat Mar 26 06:19:35 CET 2016
Hi,
I have now read an introductory text on regression and I think I do
understand what the intercept is doing. However, my original question is
still unanswered. I understand that the intercept term is the constant
that each other term is measured against. I think baseline is a good word
for it. However, it does not represent any one of the x variables by
itself. Is there a way in R, to extrapolate the individual x variable
intercepts from the equation somehow.
On Tue, Mar 15, 2016 at 8:26 PM, David Winsemius <dwinsemius at comcast.net>
wrote:
>
> > On Mar 15, 2016, at 1:27 PM, Michael Artz <michaeleartz at gmail.com>
> wrote:
> >
> > Hi,
> > I am trying to use the summary from the glm function as a data source.
> I
> > am using the call sink(<some file>) then
> > summary(logisticRegModel)$coefficients then sink().
>
> Since it's a matrix you may need to locate a function that write matrices
> to files. I seem to remember that the MASS package has one.
>
> > The independent
> > variables are categorical and thus there is always a baseline value for
> > every category that is omitted from the glm output.
>
> Well, it's not really omitted, so much as shared among all variables. For
> further reading in the halp pages consult:
>
> ?model.matrix
> ?contrasts
> ?contr.treatment
>
> But you probably need to supplement that with an introductory text that
> covers R regression defaults.
>
> > I am interested in how
> > to get the Z column for all of the categorical values.
>
> The Z column? You meant the "z value" column. Again, since it's a matrix
> you need to use column indexing with "["
>
> summary(logisticRegModel)$coefficients[ , "z value"]
>
> Read up on the summary function for glm objects at:
>
> ?summary.glm
>
>
> > I don't see any row
> > for the reference category.
>
> What do you imagine the (Intercept) row to be doing? If you are having
> difficulty understanding this (which is not really an R-specific issue)
> there are probably already several explanations to similar questions on:
>
> http://stats.stackexchange.com/
>
>
> >
> > How can I get this Z value in the output?
>
> Asked and answered.
>
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
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> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius
> Alameda, CA, USA
>
>
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