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Thread: Help with Interactaction Assesment

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    Unhappy Help with Interactaction Assesment




    Hello!

    Can anyone explain why my Breslow-Day test for interaction was significant (p=0.0005) but my forward selection logistic regression test for the same interaction was not significant (p=0.10). Should I increase my p threshold for the logistic regression test? If yes, should I not be concerned that my interaction may be a false positive?

    Thanks!
    Confused

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    Re: Help with Interactaction Assesment

    Dont use programs to build models unless you have thousands of covariates, no hypotheses and theory.

    Just build a model yourself and see what turns out.
    Stop cowardice, ban guns!

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    Re: Help with Interactaction Assesment

    Thanks for the reply hismith! Can you elaborate?

    The data I am using is from a large national survey. I used SAS to do the above tests.

    Naxaris

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    Re: Help with Interactaction Assesment

    First describe by what you mean by forward selection?
    Stop cowardice, ban guns!

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    Re: Help with Interaction Assesment

    What I mean is that I compare a reduced model (main effects) with a model that contains the interaction I am interested in. If the Likelihood Ratio Test has a p value of less than 0.05 then I include that interaction and use the new model as my reduced model when testing the next interaction.

    In my situation I first did a BD test (which was yes to interaction) and then I did a logistic regression test for interaction and got a p value of 0.10. I don't understand the opposing results. What should I conclude?

    I am doing a graduate level course in Epidemiology - which is why I am using multiple tests to test for interaction.

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    Re: Help with Interactaction Assesment

    What variables are in your logistic model besides x1, x2, x3 (the interaction of two binary variables) ?

    I thought your first post was saying you were doing stepwise or something like that.

    What university are you at?
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    Re: Help with Interactaction Assesment

    Its a uni in Canada which you may not know since it looks like your in the US.

    My covariates are not all binary, for example the interaction I am interested in would be between a binary exposure and a categorical predictor (income).

    Would you know why the two tests do not align?

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    Re: Help with Interactaction Assesment


    Figured it out!

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