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From |
Austin Nichols <austinnichols@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Xtivreg2: Dropping dummy variables due to Collinearity |

Date |
Tue, 14 Jun 2011 11:12:23 -0400 |

Shonda Naples <liminalzest@gmail.com>: Dropping an intercept is typically not an option for XT commands, for obvious reasons. On Tue, Jun 14, 2011 at 10:56 AM, Shonda Naples <liminalzest@gmail.com> wrote: > An alternative to what Maarten suggests, you could drop the intercept > term and retain all the dummies. > > On Tue, Jun 14, 2011 at 9:52 AM, Maarten Buis <maartenlbuis@gmail.com> wrote: >> On Tue, Jun 14, 2011 at 3:27 PM, vikramfinavker wrote: >>> I am using xtivreg2 and the regression is dropping my dummy variables for >>> year due to collinerarity. I have 10 year dummy: >> >>> In normal regression (reg) it omits yr99 and yr00 saying there is >>> collinearity but in xtivreg2 it drops yr99 and yr09 saying they are >>> collinear. >>> >>> Could someone please explain me whats wrong here? Is it my data? >> >> When a set of variables are perfectly colinear Stata cannot >> distinguish between them, so it is pretty much random which variables >> it will exclude. For predictions it won't matter (which is why Stata >> cannot distinguish between them), but for interpretation of your >> results it matters a lot. A computer cannot know how you want to >> interpret your results. So if you don't tell it, the computer must >> ignore that consideration. So, you must tell Stata how you want to >> interpret your year dummies. Dummies are (usually, but there are >> exceptions) comparisons of groups in your case years, so you must tell >> Stata which year you want to compare with which other year. You >> typically do so by leaving out one year dummy, which is the reference >> category (but there are other ways of doing it). All remaining year >> dummies are comparison with that reference category. * * 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/

**References**:**st: Xtivreg2: Dropping dummy variables due to Collinearity***From:*vikramfinavker <vikramfinavker@gmail.com>

**Re: st: Xtivreg2: Dropping dummy variables due to Collinearity***From:*Maarten Buis <maartenlbuis@gmail.com>

**Re: st: Xtivreg2: Dropping dummy variables due to Collinearity***From:*Shonda Naples <liminalzest@gmail.com>

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