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From |
fatma bircan <bircan@metu.edu.tr> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
RE: st: RE: ln1=0 for missing values |

Date |
Wed, 21 Apr 2004 16:04:38 +0300 |

Thank you for the insightful remarks. I need to think about it a bit more I guess. ------------------ >I am not an expert on Tobit, or even a user of it. But >there is surely folklore on this problem, which sounds as >if it could arise frequently. > >You're nudging 0 to 1, in a context where expenditure is presumably >zero or positive. And presumably 1 is (substantially?) less than >the smallest positive number observed. > >The nudge is still a fudge. What you choose could vary drastically >on a log scale, which is crucial here. In other contexts, some people >use (half smallest non-zero number observed). In yet other contexts, >people loop over a range of fudges and see what difference >it makes. > >Nick >n.j.cox@durham.ac.uk > >> -----Original Message----- >> From: owner-statalist@hsphsun2.harvard.edu >> [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of fatma bircan >> Sent: 21 April 2004 13:41 >> To: statalist@hsphsun2.harvard.edu >> Subject: Re: st: RE: ln1=0 for missing values >> >> >> For example in a Tobit model if we make a log transformation of the >> expenditures (dep. var.) some values of the dep. var. will have >> missing values since they were originally equal to zero. But assuming >> that the zero exp. =1 and then taling the log of expenditures, we can >> estimate the tobit model. Is this OK for having extra grouns? >> >> >> ------------------- >> >Yes, there are. Unless you have extra grounds >> >for thinking that missing really means 1, >> >this practice surely cannot be recommended >> >in general. >> > >> >Nick >> >n.j.cox@durham.ac.uk >> > >> >fatma bircan >> > >> >> Is there any problems with assuming that the dependent variable >> takes >> >> the value of 1 when it is missing to make the ln(dep. var.) equal >> to >> >> zero. >> > > >* >* 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/ > Fatma Bircan Middle East Technical University Department of Economics 210-2032 xxxxxxxxxxxxxxxxxxxxxxxxxxxxx * * 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**:**RE: st: RE: ln1=0 for missing values***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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