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From |
"Daniel Schneider" <daniel.schneider@stanford.edu> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: Interaction terms in a logit model |

Date |
Fri, 18 Mar 2005 22:00:10 -0800 |

Dear List, I have read the articles by Norton, Wang, Ai (2004) as well as their more theoretical paper (Ai & Norton (2000)) and I am aware of other literature describing the same problem. I think I understood the theoretical problems and reasoning behind their approach, but unfortunately I really have a hard time of really understanding what I have to do when I use interaction terms in a logit regression. What I am trying to do is run a simple logit model with a simple interaction term, something like this: Y = b1X1 + b2X2 + b3X1X2 + controlling_variables Where Y is a 0/1 variable. I can run inteff, but I am just not able to interpret the results: What does it mean that the effect is varying across the predicted probability? My problem is that I would like to just do a -predict- command, generate some simple graphs that show the different behavior of the predicted probability depending on the manipulation of the two variables (e.g., if X2 is a binary dummy, I would get two lines running from left to right, when the yaxis is my predicted probability and the xaxis is every value that X1 can take). To achieve this, I used something like -prvalue- (or -prgen-) and just plotted the predicted results later on. My understanding from the articles tells me that this might be inaccurate, but I am now even confused about that. So, if anyone can help me in interpreting the results of inteff beyond saying something like "for some probabilities b3 is significant for others it is not" - I can do that but I am not sure what that MEANS for my model, because as far as I can see it I just want to show the readers of my paper how a specific variable might have different influences depending on a moderating variable. How can I show this in graphs or data tables? (I also read the DeLeire (2000) paper mentioned by Norton, Wang and Ai, and I think this might be what I want to do, but I am not sure how to achieve those results properly). I really appreciate any help... Daniel Schneider * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Interaction terms in a logit model***From:*Richard Williams <Richard.A.Williams.5@nd.edu>

**Re: st: Interaction terms in a logit model***From:*"maartenbuis" <maartenbuis@yahoo.co.uk>

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