Hi Thierry, Thanks for your quick answer. The problem is not so much the LABOUR variable, however, but the AGE variable, which consists of about 5 categories for which I do indeed not create separate dummy variables. But R does not behave as expected when deciding on which dummy to use as reference category ...
Jos On Mon, Jan 19, 2009 at 2:37 PM, ONKELINX, Thierry <thierry.onkel...@inbo.be> wrote: > Dear Jos, > > In R you don't need to create you own dummy variables. Just create a > factor variable LABOUR (with two levels) and rerun your model. Then you > should be able to calculate all coefficients. > > HTH, > > Thierry > > ------------------------------------------------------------------------ > ---- > ir. Thierry Onkelinx > Instituut voor natuur- en bosonderzoek / Research Institute for Nature > and Forest > Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, > methodology and quality assurance > Gaverstraat 4 > 9500 Geraardsbergen > Belgium > tel. + 32 54/436 185 > thierry.onkel...@inbo.be > www.inbo.be > > To call in the statistician after the experiment is done may be no more > than asking him to perform a post-mortem examination: he may be able to > say what the experiment died of. > ~ Sir Ronald Aylmer Fisher > > The plural of anecdote is not data. > ~ Roger Brinner > > The combination of some data and an aching desire for an answer does not > ensure that a reasonable answer can be extracted from a given body of > data. > ~ John Tukey > > -----Oorspronkelijk bericht----- > Van: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > Namens Jos Elkink > Verzonden: maandag 19 januari 2009 15:16 > Aan: r-help@r-project.org > Onderwerp: [R] reference category for factor in regression > > Hi all, > > I am struggling with a strange issue in R that I have not encountered > before and I am not sure how to resolve this. > > The model looks like this, with all irrelevant variables left out: > > LABOUR - a dummy variable > NONLABOUR = 1 - LABOUR > AGE - a categorical variable / factor > VOTE - a dummy variable > > glm(VOTE ~ 0 + LABOUR + NONLABOUR + LABOUR : AGE + NONLABOUR : AGE, > family=binomial(link="logit")) > > In other words, a standard interaction model, but I want to know the > intercepts and coefficients for each of the two cases (LABOUR and > NONLABOUR), instead of getting coefficients for the differences as in > a normal interaction model. > > But the strange thing is, for the two occurances of the AGE variable, > it makes a different choice as to which AGE category to leave out of > the regression. The cross-table of AGE with LABOUR does not have empty > cells. > > Anyone any idea what might be going wrong? Or what I could do about > this? > > Thanks in advance for any help! > > Regards, > > Jos > > -- > Johan A. Elkink > Lecturer > School of Politics and International Relations & CHS Graduate School > University College Dublin > Ph. +353 1 716 7026 | Library Building, Rm 512 > http://jaeweb.cantr.net > > ______________________________________________ > R-help@r-project.org 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. > > Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer > en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd > is > door een geldig ondertekend document. The views expressed in this message > and any annex are purely those of the writer and may not be regarded as > stating > an official position of INBO, as long as the message is not confirmed by a > duly > signed document. > -- Johan A. Elkink Lecturer School of Politics and International Relations & CHS Graduate School University College Dublin Ph. +353 1 716 7026 | Library Building, Rm 512 http://jaeweb.cantr.net ______________________________________________ R-help@r-project.org 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.