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Re: st: Re: Adding the marginal effects at individual values of


From   "Solomon Tesfu" <ecosttx@langate.gsu.edu>
To   <baum@bc.edu>
Subject   Re: st: Re: Adding the marginal effects at individual values of
Date   Mon, 22 Feb 2010 20:26:31 -0500

I'm sorry about this but I'm not sure why the MEs calculated at -60, -59, -58,...,58, 59, 60 should be  related to those at -6.0,  -5.9, -5.8,..., 5.8, 5.9, 6.0 in a heavily non-linear model like probit . Are you suggesting that they are equivalent or proportional or...?

Thanks again,

Solomon  

>>> Christopher Baum <baum@bc.edu> 02/22/10 1:33 PM >>>
As I said in an earlier message, you can do this on a fine grid.  
Multiply the variable of interest by 10 and it will range from -60 to  
+60, and you can step through those 120 integers and calculate AMEs  
for each of them, corresponding to the original variable evaluated at  
-6.0, -5.9, -5.8, ...

I suggest making integer-valued 'buckets' out of this to make exact  
comparisons hassle-free.

Kit Baum   |   Boston College Economics and DIW Berlin   |   http://ideas.repec.org/e/pba1.html
An Introduction to Stata Programming   |   http://www.stata-press.com/books/isp.html
An Introduction to Modern Econometrics Using Stata   |   http://www.stata-press.com/books/imeus.html

On Feb 22, 2010, at 1:09 PM, Solomon Tesfu wrote:

> Thanks again for your helpful suggestions . When I said the AME does  
> not show the variations in the ME at various levels of the regressor  
> I was refering to the AME calculated using the entire set of  
> observations. Yes, I can see the pattern in the AME by calculating  
> it for successively increasing intervals of the observed values of  
> the regressor. But my undertanding of the syntax you suggested was  
> that it calculates the MEs at only integer points (not the AMEs for  
> intervals of values) and adds them to the data as an additional  
> variable. The observed values of my variable of interest range  
> between -6 and 6 and the sample size is 2400. If I round off all the  
> observed values to the nearest integers and calculate the MEs only  
> at integer points that will still be informative but will hide some  
> details. Anyway, I think I have sufficient inputs from you guys and  
> I'll work on it.
>
> Solomon
>
>>>> Kit Baum <baum@bc.edu> 02/22/10 7:27 AM >>>
> On Feb 22, 2010, at 2:33 AM, Solomon wrote:
>
>> Thanks again Kit and Richard, for your ideas. I understand that I  
>> cannot talk about precision of the estimates  at each point of  
>> observation but once I get the estimates I can plot them against  
>> the values of the variable and look at the pattern. This is  
>> important because I have a reason to believe that the marginal  
>> effects  will be different at high and low values of the regressor  
>> and the AME or the marginal effect at mean do not help me to verify  
>> this possibility.
>
> I don't see, then, how calculating AMEs at various points in the  
> regressor space would not 'verift this possibility'. If you take the  
> continuous variable you have and 'bin' it into ranges---which can be  
> as many as you can handle, given matsize---you can calculate the  
> AMEs at very-very-low, very-low, low, low+, low++, low+++, etc.  
> values of that regressor. Depending on your sample size and the  
> capacity of Stata (e.g., Stata/SE or Stata/MP can handle larger  
> matrices) you could calculate AMEs on a very fine grid of values of  
> the regressor, and 'look at the pattern'. Why does this not answer  
> the question you'd like to pose to the data?
>
> If AMEs differ across levels of income, I don't need to use an  
> income of $54,321 to verify that. An income of $55,000 would work,  
> as long as its AME is clearly distinct from that of income = $5,000.
>
> Kit Baum   |   Boston College Economics & DIW Berlin   |   http://ideas.repec.org/e/pba1.html
>                              An Introduction to Stata Programming   
> |   http://www.stata-press.com/books/isp.html
>   An Introduction to Modern Econometrics Using Stata  |   http://www.stata-press.com/books/imeus.html
>
>
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