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| From | "Tim Burnett (ECO)" <Tim.Burnett@uea.ac.uk> |
| To | "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |
| Subject | st: Setting the base group in dummy variable interaction terms |
| Date | Sun, 30 Sep 2012 11:04:35 +0000 |
Dear all, I have a question which may b trivially easy to answer but unfortunately I can't find it. I am using a random effects probit model as follows: xtprobit switched ib4.service ib1.supplier ib2.duration bundled numberservs i.supplier#i.service i.bundled#ib1.supplier i.bundled#ib4.service ib1.income ib1.employment i.children i.gender ib1.education ib2.age if INCLUDEVAR==1, re Which obviously includes many dummy variables. I am using the prefix ib#. to set the base category for the dummy variables for the standalone dummies. Unfortunately this isn't working for the dummy interaction terms which I would like to be based upon the excluded categories of the standalone variables (4 for service, 1 for supplier) since in these cases the excluded category has specific relevance in terms of understanding the results.. Placing, respectively, ib1 and ib4 in the command above doesn't seem to do any harm, but Stata just ignores it as follows: note: 1.bundled#6.supplier omitted because of collinearity note: 1.bundled#4.service omitted because of collinearity It ignores my base category request. Any suggestions? Many thanks, Tim -- Tim Burnett PhD Researcher Department of Economics & ESRC Centre for Competition Policy University of East Anglia Email: tim.burnett@uea.ac.uk Phone: +44 (0) 7793 116 522 Skype: timb318 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/