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From |
John Hendrickx <john_hendrickx@yahoo.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: dummy variables with desmat |

Date |
Fri, 20 Aug 2004 02:58:12 -0700 (PDT) |

Desmat creates dummy variables for variables and interactions without checking whether any of these are duplicates. Desmat then uses the Stata command _rmcoll to delete the duplicates. Desmat doesn't renumber the dummies, desrep prints descriptive labels anyway. Which particular dummies are dropped is determined by _rmcoll. It usually deletes the second and subsequent duplicates but it can also drop highly collinear (dummy) variables (and that's actually what it's for). If you use the option "defcon(dir)" then all the variables in your model will be treated as continous. Whether or not you specify this option should strongly affect your model and the desmat output. The "desrep(all)" option on the other hand determines which statistics are printed. It shouldn't affect which dummies are dropped. I'd suggest running desmat using the "colinf" option. It will tell you which dummies have been dropped, maybe that will help. For use in a loop, you might want to use desmat as a standalone command to create dummies, then using "renpfix _x_ _z_". Then you can use _z_* in subsequent models using desmat as a prefix command and adding whatever extra terms you want. Something like desmat var1 var2 varn renpfix _x_ _z_ desmat: logistic y _z_* new1 desmat: logistic y _z_* new2 Hope this helps, John Hendrickx --- Tim Wade <wade_tj@yahoo.com> wrote: > Hello Statalisters: > > I have recently been using John Henrickson's excellent > and much needed "desmat" program for some logistic > regressions. When I run a model with over 10 or so > variables, together with either the desrep(all) or the > defcon(dir) options, the order of the dummy variables > (_x_1 _x_2, etc.) created changes from the order in > which they were specified in the model. If I do not > use either the desrep or the defcon options, the order > of the dummy variables created is the same as the way > I specified the model. In other words, the dummy > variable represented by the second term is no longer > _x_2. This is troubling because I am trying to > automate a loop to run the same linear combinations > with every model while controlling for different > factors. Is this a feature of the command? If so, why > does the order of these variables change. > > Thanks very much for any insights, Tim > > > ===== > wade_tj@yahoo.com > > > > _______________________________ > Do you Yahoo!? > Win 1 of 4,000 free domain names from Yahoo! Enter now. > http://promotions.yahoo.com/goldrush > * > * For searches and help try: > * http://www.stata.com/support/faqs/res/findit.html > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > __________________________________ Do you Yahoo!? Yahoo! Mail is new and improved - Check it out! http://promotions.yahoo.com/new_mail * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: dummy variables with desmat***From:*Tim Wade <wade_tj@yahoo.com>

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