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From |
Maarten buis <[email protected]> |

To |
[email protected] |

Subject |
Re: AW: st: AW: beta coefficients for interaction terms |

Date |
Mon, 22 Jun 2009 09:33:24 +0000 (GMT) |

--- On Sat, 20/6/09, [email protected] wrote: > Why do I have to standardize the dependent variable as > well? If I standardize it, the constant won't be > significant anymore. Without standardizing the constant > is highly significant in my case. This is not surprising, actually we a-priori know that that constant should be exactly zero (which is the null-hypothesis that the reported significance level tests). This is easiest to see in a bivariate regression between y and x. In this case there a couple of properties that are relevant: 1) If we standardize a variable then the mean will become 0. 2) If we fit a regression then the regression line will go through the point [mean(x), mean(y)] 3) The constant is the y-value on the regression line when x equals zero Combining properties 1) and 2) we know that a standardized regression line will go through the point (0,0). Combining this with propery 3) shows that the constant of a standardized standardized regression line is by definition equal to zero. To answer your question, I would say that if you want to report standardized coefficients you should standardize both the dependent and indpendent variables, not because there is some magical/statistical Law that proscribes it, but because this is what is meant with standardization in most disciplines. If you do it differently you will just cause confusion with your readers. -- Maarten ----------------------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://home.fsw.vu.nl/m.buis/ ----------------------------------------- * * 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/

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