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From |
Richard Williams <richardwilliams.ndu@gmail.com> |

To |
statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu |

Subject |
Re: Re: st: What is the effect of centering on marginal effects? |

Date |
Thu, 02 Aug 2012 10:29:53 -0500 |

At 08:41 AM 8/2/2012, Alessandro Freire wrote:

Dear all, Indeed, centering variables will inevitably result in different coefficients and standard errors compared to an uncentered model. Even though, this is due to the fact that these coefficients correspond to different quantities of interest in each model. That is, a centered model is no more "accurate" than an uncentered model. If we estimated the marginal effect of a one unit change in X at a given value of Z from the estimates of both centered and uncentered models, we would obtain the same results. One should not confuse coefficients with effects ( see Kam & Franzese, "Modeling and Interpreting Interactive Hypotheses in Regression Analysis: A Refresher and Some Practical Advice" 2005). Thus, centering variables brings no meaningful changes whatsoever, since it adds no new information to the estimation of parameters. Centering was a common procedure during the 1980s due to computational imprecision issues, but it makes little sense, if any, nowadays. Alessandro

reg y x

Suppose instead you do reg y xcentered

Part of the reason I bring this up -- I've seen students look at models like reg y female x reg y female x female*x

I discuss these issues more in this handout: http://www.nd.edu/~rwilliam/stats2/l53.pdf ------------------------------------------- Richard Williams, Notre Dame Dept of Sociology OFFICE: (574)631-6668, (574)631-6463 HOME: (574)289-5227 EMAIL: Richard.A.Williams.5@ND.Edu WWW: http://www.nd.edu/~rwilliam * * 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/

**Follow-Ups**:**Re: Re: st: What is the effect of centering on marginal effects?***From:*Ulrich Kohler <kohler@wzb.eu>

**References**:**Re: Re: st: What is the effect of centering on marginal effects?***From:*Christopher Baum <kit.baum@bc.edu>

**Re: Re: st: What is the effect of centering on marginal effects?***From:*Alessandro Freire <alessandro.freire@gmail.com>

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