Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

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


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/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index