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

 From fatma bircan 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.
>> >
>
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>
Fatma Bircan
Middle East Technical University
Department of Economics
210-2032

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```