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Re: st: tobit interpretation
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: tobit interpretation
Date
Thu, 1 Aug 2013 08:48:14 +0100
Why do you see Tobit as the appropriate model here? Tobit is for
situations where values could have been outside certain limits but
were reported only within those limits. That's quite different from a
case where values can only exist within those limits. Your problem
sounds like most a logit model for proportions as dependent variable.
For a concise and lucid introduction to this field see
SJ-8-2 st0147 . . . . . . . . . . . . . . Stata tip 63: Modeling proportions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. F. Baum
Q2/08 SJ 8(2):299--303 (no commands)
tip on how to model a response variable that appears
as a proportion or fraction
accessible at http://www.stata-journal.com/article.html?article=st0147
As it is, the -tobit- results do imply that you are fitting a
qualitatively incorrect model.
Nick
[email protected]
On 1 August 2013 03:29, Christine E. Boyle
<[email protected]> wrote:
> Hello,
>
> I am estimating the effect of village education level (portion of villagers
> who attended middle school) on share of village investment by the villagers
> using a tobit estimator. Dependant and independent variables are both
> between 0 and 1.
>
> Once I set the ul (1) and the ll(0), negative coefficients return such as
> "-4.985241"
>
> xttobit vl_share edu_vill, ul(1) ll(0) i(countycode)
>
> Coef. =Std. Err. z
> P>z [95% Conf.Interval]
>
> edu_vill -4.985241 2.46903 -2.02
> 0.043 -9.824451 -.1460307
>
> How does one interpret the coefficient that is outside of the bounds placed
> on the model?
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