From: John Fox <jfox_at_mcmaster.ca>

Date: Sat 14 Oct 2006 - 17:25:01 GMT

John Fox

Department of Sociology

McMaster University

Hamilton, Ontario

Canada L8S 4M4

905-525-9140x23604

http://socserv.mcmaster.ca/jfox

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Sun Oct 15 03:28:23 2006

Date: Sat 14 Oct 2006 - 17:25:01 GMT

Dear Katja,

If the fitted values are the same and the coefficients differ, then the parametrization of the models differ. I suspect that SPSS is using sum-to-zero contrasts (contr.sum in R, coded -1, 0, 1), while R uses dummy-coded contrasts (contr.treatment, coded 0,1) by default. If this is the case, then you should get the same coefficients in R by setting options(contrasts=c("contr.sum", "contr.poly")). There are other ways of doing this as well.

See ?options, ?contr.treatment, etc., and section 11.1.1 of the introductory manual that comes with R (and perhaps read something more detailed about how R handles factors in linear models).

I hope this helps,

John

John Fox

Department of Sociology

McMaster University

Hamilton, Ontario

Canada L8S 4M4

905-525-9140x23604

http://socserv.mcmaster.ca/jfox

> -----Original Message-----

*> From: r-help-bounces@stat.math.ethz.ch
**> [mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Katja
**> Walentowitz
**> Sent: Saturday, October 14, 2006 11:08 AM
**> To: Dirk Eddelbuettel
**> Cc: r-help@stat.math.ethz.ch
**> Subject: Re: [R] Differences in estimates calculated in R and SPSS
**>
**> I have compared the models, they are exactly the same. The
**> same for the data. The problem occurs most often when I use
**> the aov-function.
**> When I calculate the fitted values, they are the same, but
**> the intercept is somewhat different. In R the intercept is
**> more or less the mean of the regressand values, as defined in
**> some statistical books - but still: it is not the exact mean.
**> In SPSS it is not.
**>
**> Thanks again for helping me.
**> Katja
**>
**> On 10/14/06, Dirk Eddelbuettel <edd@debian.org> wrote:
**> >
**> >
**> > On 14 October 2006 at 16:59, Katja Walentowitz wrote:
**> > | I am a bit confused because I get different estimates for the
**> > | regression coefficients from R and SPSS.
**> > | Does anyone have an explanation for this? As I am not so
**> > | experienced in data analysis, I don't know why this happens.
**> >
**> > Maybe you are not estimating the same model -- one may have an
**> > intercept, and the other doesn't. Or maybe something happens while
**> > you read the data -- start by comparing summary statistics,
**> > tabulations and plots of your data.
**> >
**> > But as you didn't tell what you estimated, and how, it is a
**> tad hard
**> > for use to guess. There is a Posting Guide recommending
**> how to phrase
**> > questions and what to suplly ...
**> >
**> > Dirk
**> >
**> > --
**> > Hell, there are no rules here - we're trying to accomplish
**> something.
**> > -- Thomas
**> A. Edison
**> >
**>
**> [[alternative HTML version deleted]]
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide
**> http://www.R-project.org/posting-guide.html
**> and provide commented, minimal, self-contained, reproducible code.
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Sun Oct 15 03:28:23 2006

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