st: marginal effects for polynomial regressions

["Bischof, Daniel" <db308@leicester.ac.uk>]

Hi,

I'm currently running a polynomial regression and I'm trying to calculate marginal effects using the margin command. Therefore my regression model is as follows: 

Y = a + b1*x1+ b2*x1^2 + controls (1)

Putting this into a stata command turns out to be the following:

reg c.x##c.x + controls (2)

Then I calculated the margins by using the following:

margins, over(x) at((means) controls) (3)

And the marginsplot by using: 

marginsplot (4)

Yet, I'm not sure the last two commands will do the deal (3+4), since I'm not sure whether stata is then calculating the derivate of function (1) or just for the very first part of the expression (b1x1). I hope somebody can help me out on this! 

Thank you very much in advance,
		
Daniel
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