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
>[email protected]
>
>> -----Original Message-----
>> From: [email protected]
>> [mailto:[email protected]]On Behalf Of fatma
bircan
>> Sent: 21 April 2004 13:41
>> To: [email protected]
>> 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
>> >[email protected]
>> >
>> >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/
