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From |
Maarten Buis <maartenlbuis@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Quadratic Function, Turning Points and Interaktion Terms |

Date |
Wed, 9 May 2012 10:19:41 +0200 |

On Tue, May 8, 2012 at 9:54 PM, Lukas Borkowski wrote: > I work on a model that can be simplified as y = a_x1 b_x2 c_x3 > My first findings suggest that the effects of x1-3 on y will change with increases in x1-3. Now, do I have to run > reg y x1 x1sq > di _b[x1]/(2*_b[x1sq])*-1 > for every x seperately or combined, thus > reg y x1 x1sq x2 x2sq x3 x3sq > in order to find the correct turning points? That depends on whether or not you want to the turning points adjusted for the other variables. There can be no general answer to that, it just depends on your problem, your question, your theory, etc. > What happens when I add interaction terms, lets say for g1 and g2 for groups. > Should I run the regression over my unrestricted equation including all interaction terms? That depends on what you want to do and how much information is present in your data. Rather than trying to find "The Answer" I would look substantively at what I want to learn from the data, what information is present in the data, and how I can combine the two in a sensible argument. You may also find the following link useful: <http://www.maartenbuis.nl/wp/inter_quadr/inter_quadr.html> Hope this helps, Maarten -------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://www.maartenbuis.nl -------------------------- * * 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/

**References**:**st: Quadratic Function, Turning Points and Interaktion Terms***From:*Lukas Borkowski <LukasBork@hotmail.com>

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