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From |
"Jesper Lindhardsen" <JESLIN01@geh.regionh.dk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: Understanding Factor variables - is order significant ? |

Date |
Thu, 27 May 2010 09:33:43 +0200 |

I'm very happy with for the first (out of uncountable occasions) Stata is wrong !!!! Do you get a "find a bug" T-shirt ;-) I'm looking forward to a fix as I find the factor variable feature extremely useful. Jesper Jesper Lindhardsen MD, Ph.d. student Department of Cardiovascular Research Copenhagen University Hospital, Gentofte Denmark -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Richard Williams Sent: 27. maj 2010 00:45 To: statalist@hsphsun2.harvard.edu Subject: Re: st: Understanding Factor variables - is order significant ? You wonder how such an obvious problem could be missed. :) Actually, I think this should be a strong contender for most esoteric bug of the year award! Thanks for fixing it. At 03:17 PM 5/26/2010, Roberto G. Gutierrez, StataCorp wrote: >Jesper (and those others who have contributed on this thread) have discovered >a bug in how factor-variable interactions are being parsed in Stata. The >specific conditions that trigger this are as follows: > > 1. You specify a simple interaction (a single # sign) between two or more > factor variables. > > 2. The first variable in the interaction has the value zero as one of > its categories. > > 3. The first specification in the interaction has a base level that is > not the default of zero (the lowest level for the first variable). > > 4. At least one of the remaining variables in the interaction has a base > equal to the lowest-valued category for that variable, > whether expicitly > specified or taken as the default. > > 5. Almost all estimation commands are affected by this bug, with -regress- > being one notable exception. > >When the above conditions occur, Stata is attempting to omit an extra cell in >the interaction. Sometimes, the cell will be omitted altogether, other times >Stata will produce a coefficient for that cell, but missing standard errors >and confidence intervals. Either way, the model fit is thrown off because the >cell's coefficient is not properly estimated. > >We will fix this in the next executable update, to be made available soon. > >--Bobby --Jeff >rgutierrez@stata.com jpitblado@stata.com >* >* 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/ ------------------------------------------- Richard Williams, Notre Dame Dept of Sociology OFFICE: (574)631-6668, (574)631-6463 HOME: (574)289-5227 EMAIL: Richard.A.Williams.5@ND.Edu WWW: http://www.nd.edu/~rwilliam * * 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/ * * 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**:**Re: st: Understanding Factor variables - is order significant ?***From:*rgutierrez@stata.com (Roberto G. Gutierrez, StataCorp)

**Re: st: Understanding Factor variables - is order significant ?***From:*Richard Williams <richardwilliams.ndu@gmail.com>

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