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From |
<ELAZZARI@clinic.ub.es> |

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

Subject |
RE: st: multivariable median regression |

Date |
Sat, 23 Apr 2005 17:11:58 +0200 |

Thank you Joe, Actually, I use the bsqreg. I couldn't find any reference to which test I can use to compare nested models (for ex. the full model with a model without a variable). I can't apply a loglikelihood ratio test, since there's no likelihood estimation. I was wondering about an F test, based on the median regression's pseudo R2, but I couldn't work it out. So, any help is greatly appreciated. Elisa -----Mensaje original----- De: Jhilbe@aol.com [mailto:Jhilbe@aol.com] Enviado el: vie 22/04/2005 23:19 Para: statalist@hsphsun2.harvard.edu CC: Asunto: Re: st: multivariable median regression You asked about how to run a multivariate median regression. Isn't this the same as Stata's qreg command. If you type . search median regression at the Stata prompt, a lists of references appears. One reference is for a Frequently Asked Questions source related to qreg. Here is the first two paragraphs from the FAQ. If this is what you're looking for, then qreg is your answer. ======= "Stata's qreg command fits quantile (including median) regression models, also known as least-absolute value (LAV) models, minimum absolute deviation (MAD) models, and L1-norm models. "Median regression estimates the median of the dependent variable, conditional on the values of the independent variable. This is similar to least-squares regression, which estimates the mean of the dependent variable. Said differently, median regression finds the regression plane that minimizes the sum of the absolute residuals rather than the sum of the squared residuals." ======= Joe Hilbe =========================================================: Dear listusers, I have to build a multivariable median regression model but I don't understand which is the appropriate method to select variables. I can get the pseudo R2 that is based on the likelihood of a double exponential distribution, but I don't know how to use this information to decide if a variable has to enter or not in the equation. Many thanks, Elisa <mailto:elazzari@clinic.ub.es> -----Mensaje original----- De: wying1@umbc.edu [mailto:wying1@umbc.edu] Enviado el: vie 22/04/2005 20:18 Para: statalist@hsphsun2.harvard.edu CC: Asunto: st: problem with missing F stats and P values in joint model test Dear listusers, When I run multivariate regression, the F or chi2 model statistic has been reported as missing for some models. The Stata help menu says "the model that you estimated has its F or chi2 model statistic reported to be missing. Stata has done that so as not to be misleading, not because there is something necessarily wrong with your model". But I want to understand the mechanism behind this problem. I suspect it might be due to the lack of LHS vars' variation or lack of statistical power. Does anybody have experienced the same problem and have some thoughts to share? What kind of consequence will this cause? Does it affect the interpretation? Many thanks, Ying * * 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/ * * 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/

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