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| From | Philip Ender <ender97@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: Re: st: RE: problem with factor variable and margins. |
| Date | Wed, 17 Mar 2010 11:01:06 -0700 |
Rich wrote: >I think I have tracked down the problem. In addition to the factor variable nainc, I have a continuous variable nainc_ainc as a regressor (which is the >indicator times a continuous variable). The margins command then got confused and assumed that nainc was an abbreviation for nainc_ainc, which did >appear in the results and subsequent tests. When I rename nainc_ainc as n2ainc_ainc, my problem goes away -- a marginal effect for the discrete >change in the factor variable nainc does indeed show up in the results. > >If I am right in diagnosing why the rename solves the problem, this means there is a bug in stata's margins. It is not reporting an ambiguous >abbreviation, it is simply picking one. Should I report it to stata's tech staff, or is that something you do, Martin? I don't think the problem is with -margins- but with the fact that you created the interaction outside of your model. If you create the interaction using the factor variables in the model then -margins- not only identifies all of the terms but produces marginal effects that take into account the interactions. Without reproducing you entire model, it would look something like this: . tobit dv i.naic c.ainc i.naic#c.ainc ... Phil -- Phil Ender UCLA Statistical Consulting Group * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/