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From |
"JVerkuilen (Gmail)" <jvverkuilen@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Prediction at the 'mean' of a categorical- xi3? |

Date |
Thu, 14 Mar 2013 00:35:57 -0400 |

On Wed, Mar 13, 2013 at 11:59 PM, <graupel75@gmail.com> wrote: > JVerkuilen writes: > > I've used both -xi3- center option and generated the mean-centered var > by hand, and run the regression with this new var, but the log lik and > AIC/BIC are quite different indicating that more than just the ref > category has changed... > so I must be confused. > > Let's say I have a categorical (levels 1 to 6), do I then estimate > with the mean-centered value as a continuous var, and predict at 3.5? > This doesn't make so much sense as it would assume the steps between > levels are equivalent; I've looked in both Agressi and Long's Stata > book without success- Sounds to me like you're treating that as one variable, but it's really six categories which you need to subject to a rank 1 restriction of some sort, which means this needs to be represented as five variables. (IMO calling a multicategory grouping a variable is highly misleading.) That rank 1 constraint could be that the group size weighted average of them is 0, which is like effects coding but a bit more complex. I think that might be what you want. Jay * * 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/

**References**:**Re: st: Prediction at the 'mean' of a categorical- xi3?***From:*graupel75@gmail.com

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