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From | John Antonakis <John.Antonakis@unil.ch> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: What is the effect of centering on marginal effects? |
Date | Fri, 03 Aug 2012 04:59:26 +0200 |
Hi Kit:I don't believe you are using the right vif. Should it not be the -uncentered- option in vif for both regressions below? In this case the vifs are the same.
Also see:Echambadi, R., & Hess, J. D. 2007. Mean-centering does not alleviate collinearity problems in moderated multiple regression models. Marketing Science, 26(3): 438-445.
Kromrey, J. D., & Foster-Johnson, L. 1998. Mean centering in moderated multiple regression: Much ado about nothing. Educational and Psychological Measurement, 58(1): 42-67.
Best, J. __________________________________________ Prof. John Antonakis Faculty of Business and Economics Department of Organizational Behavior University of Lausanne Internef #618 CH-1015 Lausanne-Dorigny Switzerland Tel ++41 (0)21 692-3438 Fax ++41 (0)21 692-3305 http://www.hec.unil.ch/people/jantonakis Associate Editor The Leadership Quarterly __________________________________________ On 02.08.2012 14:38, Christopher Baum wrote: > <> > On Aug 2, 2012, at 2:33 AM, Alessandro wrote: > >> Centered and uncentered models are algebraically equivalent (see >> Brambor et al, "Understanding Interaction Models: Improving Empirical >> Analyses" 2006). The only difference is that, in an uncentered model, >> the coefficient of b1 corresponds to the marginal effect of a one unit >> change in X when the conditioning variable Z is zero, while the >> corresponding coefficient on the centered model gives you the marginal >> effect of a change in X when Z is at its mean. >> >> This means that centering variables will not reduce multicollinearity >> on your model.> I don't think this is quite true. See what happens to the VIF when the interacted variables are centered. Also note that the elasticity
> estimates change, and become very imprecise with centering. > > sysuse auto, clear > qui reg price length weight c.length#c.weight > estat vif > margins, eyex(_all) > // center from SSC (Jann) > center price length weight > qui reg c_price c_length c_weight c.c_length#c.c_weight > estat vif > margins, eyex(_all) > > Kit > >> Kit Baum | Boston College Economics & DIW Berlin | http://ideas.repec.org/e/pba1.html > An Introduction to Stata Programming | http://www.stata-press.com/books/isp.html > An Introduction to Modern Econometrics Using Stata | http://www.stata-press.com/books/imeus.html
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