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Re: st: How to store marginal effect value after using margin command?


From   Sergiy Radyakin <serjradyakin@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: How to store marginal effect value after using margin command?
Date   Sat, 8 Jun 2013 18:07:32 -0400

type either 'return list' or 'ereturn list' (depending on the command)
to see which results are saved after these commands. From what you
describe you are interested in matrices r(b) and e(b)

sysuse auto, clear
generate lp=log(price)
regress lp weight length headroom mpg
mfx
matrix list e(b)

Best, Sergiy

On Sat, Jun 8, 2013 at 4:50 PM, Vũ Võ <hoangvu@ueh.edu.vn> wrote:
> Hi everyone,
>
> I am writing a code in do file to calculate the marginal effect of x
> on y (log-linear model)
>
> The function form as  following:
>
> Ln(Y) = a0 + a1*X + a2*X^2  + e ----> Y = exp(a0 + a1*X + a2*X^2)
>
> So, dY/dX = (a1 + 2*a2*X)*exp(a0 + a1*X + a2*X^2)        eq(1)
>
> If I run the regression by command line as:
>
> reg lnY x c.x#c.x
>
> after that using margins command:
>
> margins, dydx(x).
>
> I will obtain the marginal effect of x on Ln(Y):  (a1 + 2*a2*X).
>
> How can I calculate the dY/dX as in eq(1) by using the do file, not
> calculating manually?
>
>
> 2. Second question is:
>
> If I use command margins, predict(p)  and obtain the results as following:
>
> Marginal effects after hetprob
>        y  = Pr(y) (predict, p)
>           =  .54284206
>  ------------------------------------------------------------------------------
>  variable |      dy/dx    Std. Err.     z    p>|z|  [    95% C.I.   ]      X
>  ---------+--------------------------------------------------------------------
>         x |   .3704576      .03237   11.44   0.000   .307015    .4339   .020114
>      xhet |  -.0736092      .02423   -3.04   0.002  -.121095 -.026124   .502716
>      off1 |  (offset1)                                                  1.00516
>      off2 |  (offset2)                                                  1.09709
>  ------------------------------------------------------------------------------
>
> The question is how to store the marginal effects value, say in this
> case is 0.3704576,
>
> in the scalar in stata?
>
>
> Thank you so much.
>
> Vo Duc Hoang Vu
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