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. ______________________________________________ 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.