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From |
"Casey P. Durand" <durandca@usc.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: conflicting results on interaction effect |

Date |
Wed, 21 Jul 2010 17:51:20 -0700 |

Simon, Yes, the coefficient of X is the relationship between X and Y when and only when Z=0. Assuming you want to leave your coefficients in their raw forms, i.e. not exponentiating them and getting odds ratios, then to understand what is happening when Z=1, you have to create a new variable in which you reverse the coding of your original Z variable, (call it Z_new) such that the old 1 becomes the new 0 and the old 0 becomes the new 1. You then have to create a new interaction term with Z_new and X , and then substitute them both into your original model. The X coefficient for this new model will now be the effect of X on Y when Z is equal to 1, using the coding scheme of your original Z variable. These two models will then provide the coefficients, p values and confidence intervals necessary to do a simple slopes analysis of your interaction. As for graphing, check out the user written command -predxcon-. This provides a very simple way to graph a continuous by categorical interaction. Hopefully this is clear enough to make sense. Casey On Wed, Jul 21, 2010 at 3:49 PM, Meng Zhao <mrzm_www@yahoo.com> wrote: > > Hello, > > I run a binomial logistic regression with an interaction variable: > > Coef. P>z > x 6.958805 0.026 > z 5.11967 0.000 > x*z -7.490387 0.034 > > x is a continuous variable, z is a dummy variable. Does this result indicate a sig. positive relationship between x and dependent variable when z is 0, and a negative relationship between x and DV when z is 1? > > The plot of this interaction shows that there is a positive relationship between x and DV for both situations (z=1 & z=0). Why this conflicts with the above result? > > Thanks. > Simon > > > > * > * 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/ * * 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: st: conflicting results on interaction effect***From:*Maarten buis <maartenbuis@yahoo.co.uk>

**References**:**st: conflicting results on interaction effect***From:*Meng Zhao <mrzm_www@yahoo.com>

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