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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 14:34:23 +0100

Chiara,

Try to be a bit more specific when explaining what you want to do...
initially you asked for a plot of the marginal effect of a contionous
variable which is what the example I sent earlier does. With a
discrete 0-1 dummy there is nothing to plot as there is only one
possible change from 0-1.

Arne

2008/7/21 Chiara Mussida <cmussida@gmail.com>:
> 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/
>
*
*   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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