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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 15:07:44 +0200

At this stage it is better to ask:
the command below only allow to get the mfx for continuous variables?
this is also because, by trying with a discrete, you get the error
message below. Again: is there a way to obtain a range for y? it would
be nice, since the dep var in my model covers a wide range if values!!

Thanks and Sorry for the absence of details below!

2008/7/21 Arne Risa Hole <arnehole@gmail.com>:
> 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/
>



-- 
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/



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