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RE: st: RE: Interpretation of quadratic terms


From   Rodolphe Desbordes <rodolphe.desbordes@strath.ac.uk>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Interpretation of quadratic terms
Date   Fri, 12 Mar 2010 11:55:42 +0000

Dear Michael,

In that case, -margins- behaviour is slightly puzzling. Could the absence of output be explained by the fact that the year 1970 did not exist in your sample?



.  sysuse nlsw88, clear
(NLSW, 1988 extract)

.
. generate year = age + 1968

.
end of do-file

. tab year

       year |      Freq.     Percent        Cum.
------------+-----------------------------------
       2002 |         53        2.36        2.36
       2003 |        260       11.58       13.94
       2004 |        257       11.44       25.38
       2005 |        225       10.02       35.40
       2006 |        219        9.75       45.15
       2007 |        234       10.42       55.57
       2008 |        208        9.26       64.83
       2009 |        222        9.88       74.71
       2010 |        160        7.12       81.83
       2011 |        165        7.35       89.18
       2012 |        163        7.26       96.44
       2013 |         78        3.47       99.91
       2014 |          2        0.09      100.00
------------+-----------------------------------
      Total |      2,246      100.00


Best regards,

Rodolphe


________________________________________
From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of Michael Norman Mitchell [Michael.Norman.Mitchell@gmail.com]
Sent: 12 March 2010 07:33
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: Interpretation of quadratic terms

Dear Rodolphe

   Thanks for your message. I think it is possible that you read a
little bit more into my message than I intended... I was not purporting
to compute marginal effects, and hence did not use the "dydx()" option.
I was just showing how to compute the predicted value of "y" for a given
value of "x". That is another way that the margins command can be used.

Best regards,

Michael N. Mitchell
See the Stata tidbit of the week at...
http://www.MichaelNormanMitchell.com

On 2010-03-11 8.32 AM, Rodolphe Desbordes wrote:
> Dear Eric,
>
> I apologise for my lack of clarity regarding the -margins- command. Even though I have hardly used it, exchanges on the Statalist have made it clear that -margins- can do many things, including the calculation of marginal effects. However Michael did not seem to have used the correct syntax; I believe that the option "dydx" must be used to obtain marginal effects.
>
>   Rodolphe
>
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of DE SOUZA Eric [eric.de_souza@coleurope.eu]
> Sent: 11 March 2010 15:01
> To: 'statalist@hsphsun2.harvard.edu'
> Subject: RE: st: RE: Interpretation of quadratic terms
>
> Dear Rodolphe,
>
> I don't have Stata 11 either. But according to the preface to the new edition of Cameron and Trivedi, Microeconometrics using Stata:
> "Second, we describe the new margins command for prediction and for computation of
> marginal effects in regression models. The margins command with options including the
> dydx() option replaces the Stata mfx command and the user-written margeff command.
> Additionally, the margins command when used in conjunction with factor variables can
> simplify computation of marginal effects in models with interactions. "
>
> So the margins command is Stata 11 does allow one to calculate marginal effects
>
> Eric de Souza
> College of Europe
> BE-8000 Brugge (Bruges)
> Belgium
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Rodolphe Desbordes
> Sent: 11 March 2010 14:59
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: RE: Interpretation of quadratic terms
>
> I do not have Stata 11 installed on this computer and I am not vary familiar with the -margins- command. However, using -margins-, you did not calculate the marginal effect but the predicted value of wage, at a given value of age.
>
>
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