st: Inflection point

["Francesco Burchi" <fburchi@uniroma3.it>]

Dear statalisters,

I have run the following IV estimates:

ivreg2 wage EDU EDUSquared X1 X2 (X3=Instrument1) X4 X5 X6 X7, robust 

I would like to calculate the inflection point of EDU (=years of
schooling). Therefore, I have used the following formula:
-b_EDU/(2*b_EDUSquared),
Is this the right way to calculate the inflection point? I am surprised
that I don't use the standard deviation in the formula. Moreover, is
there a way to show graphically the effect of EDU controlling for all
the other covariates (including the squared form and the endogenous
variable X3) and visualizing the inflection point?
Finally, should I use also the cubic form to see whether eventually
there is more than one inflection point?

I am using Stata 10.

Thanks in advance for your precious help,

Regards,
Francesco.


*
*   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/