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Re: st: mfx


From   "Chiara Mussida" <cmussida@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: mfx
Date   Mon, 21 Jul 2008 12:21:23 +0200

Thanks for all these suggestions!!
the twoway function plot perfectly works with the probit formulation.
But when I try with a biprobit it says:
; is not a twoway plot type
r(198);
without claryfing the reasons!

2008/7/19 Joao Ricardo F. Lima <jricardofl@gmail.com>:
> Arne
>
> thanks for your answer. Now I understand that x represents the mpg
> variable. I was curious because I had changed the code to:
>
> #delimit ;
> twoway (function y = _b[mpg]*normden(_b[price]*`mean_price'+
> _b[mpg]*mpg+_b[_cons]), range(mpg)) ;
> #delimit cr
>
> and the graph generated was different.
>
> Best regards,
>
> Joao Lima
>
> 2008/7/19 Arne Risa Hole <arnehole@gmail.com>:
>> Joao,
>>
>> What the code below does is plotting the marginal effect of the mpg
>> variable evaluated at different values, holding the price variable
>> constant at its mean. The x in the code represents the mpg variable -
>> see -help twoway function-.
>>
>> Perhaps this is clearer:
>>
>> sysuse auto
>> probit foreign price mpg
>> mfx
>> sum price
>> local mean_price = r(mean)
>> #delimit ;
>> twoway (function y = _b[mpg]*normden(_b[price]*`mean_price'+
>> _b[mpg]*x+_b[_cons]), range(mpg) ytitle(Marginal effect)
>> xtitle(Miles per gallon)) ;
>> #delimit cr
>>
>> Arne
>>
>> 2008/7/19 Joao Ricardo F. Lima <jricardofl@gmail.com>:
>>> Dear,
>>>
>>> sorry the simple question. I am curious why I have to use "x" instead
>>> mpg (mean) in the twoway graph (..._b[mpg]*x+_b...)? Or better, what
>>> Stata understand when I type x in this command?
>>>
>>> Thanks a lot,
>>>
>>> Joao Ricardo
>>>
>>> 2008/7/18 Arne Risa Hole <arnehole@gmail.com>:
>>>> Hi Chiara,
>>>>
>>>> How about this?
>>>>
>>>> sysuse auto
>>>> probit foreign price mpg
>>>> mfx
>>>> sum price
>>>> local mean_price = r(mean)
>>>> #delimit ;
>>>> twoway (function y = _b[mpg]*normden(_b[price]*`mean_price'+
>>>> _b[mpg]*x+_b[_cons]), range(mpg)) ;
>>>> #delimit cr
>>>>
>>>> This plots the marginal effect of the mpg variable over its range
>>>> following a probit regression. The logic is the same with -biprobit-
>>>> but the formula for the marginal effect will of course be a little
>>>> more intricate in that case.
>>>>
>>>> Arne
>>>>
>>>> 2008/7/18 Chiara Mussida <cmussida@gmail.com>:
>>>>> Dear All,nuous variab
>>>>> is there a way to "plot" the mfx of a continuous variable (after a
>>>>> biprobit) to infer its behaviour over the complete range of values and
>>>>> not only for the mean of the independent variables (which is the
>>>>> default)?
>>>>>
>>>>> Thanks
>>>>>
>>>>> --
>>>>> Chiara Mussida
>>>>> PhD candidate
>>>>> Doctoral school of Economic Policy
>>>>> Catholic University, piacenza (Italy)
>>>>> *
>>>>> *   For searches and help try:
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>>>>> *   http://www.ats.ucla.edu/stat/stata/
>>>>>
>>>> *
>>>> *   For searches and help try:
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>>>> *   http://www.ats.ucla.edu/stat/stata/
>>>>
>>>
>>>
>>>
>>> --
>>> -------------------------------
>>> Joao Ricardo Lima
>>> Professor
>>> UFPB-CCA-DCFS
>>> +553138923914
>>> -------------------------------
>>> *
>>> *   For searches and help try:
>>> *   http://www.stata.com/help.cgi?search
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>>> *   http://www.ats.ucla.edu/stat/stata/
>>>
>> *
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>>
>
>
>
> --
> -------------------------------
> Joao Ricardo Lima
> Professor
> UFPB-CCA-DCFS
> +553138923914
> -------------------------------
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>



-- 
Chiara Mussida
PhD candidate
Doctoral school of Economic Policy
Catholic University, piacenza (Italy)
*
*   For searches and help try:
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*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



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