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Re: st: mfx


From   "Arne Risa Hole" <arnehole@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: mfx
Date   Mon, 21 Jul 2008 14:00:00 +0100

Chiara,

As has been pointed out many times before on the list, the Statalist
FAQ section 3.3 says:

Say exactly what you typed and exactly what Stata typed (or did) in
response. N.B. exactly! If you can, reproduce the error with one of
Stata's provided datasets or a simple concocted dataset that you
include in your posting.

If you do that someone might be able to find the error.

Arne

2008/7/21 Chiara Mussida <cmussida@gmail.com>:
> 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:
>>>>>> *   http://www.stata.com/help.cgi?search
>>>>>> *   http://www.stata.com/support/statalist/faq
>>>>>> *   http://www.ats.ucla.edu/stat/stata/
>>>>>>
>>>>> *
>>>>> *   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/
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> -------------------------------
>>>> 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/
>>>>
>>> *
>>> *   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/
>>>
>>
>>
>>
>> --
>> -------------------------------
>> 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:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>
*
*   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/



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