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| Nicki posted on Tuesday, May 23, 2006 - 6:38 pm
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First, I must thank you all for your tremendous efforts at providing free and extensive access to your teachings--they have substatially enhanced my knowledge of these subjects and your program.
Second, I have been struggling to find examples of the kind of model I am attempting to test. I have downloaded several articles from your site and examined the Mplus examples, but I don't seem to find "exactly" what I am looking for. Would you please direct me to an article or example that might help me better understand how to:
examine interactions among continuous observed predictors of zero-inflated count outcomes over time? The interpretation of LGCM in ZIP models is difficult already (for me), but I am really stuggling to understand how I might examine/interpret interactions in this context.
Thank you so much for your time and effort,
Nicki |
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| The meaning of an interaction between two continuous observed predictors would be the same as in regular regression. This does not change because of the scale of the dependent variable. |
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| Nicki posted on Wednesday, May 24, 2006 - 8:39 am
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| Thank you for your response. Do you know of any references I might consult to see how significant interactions in the prediction of level, growth, level#1, and growth#1 might be described and discussed? I would greatly appreciate some materials to reference. My outcomes are delinquency and substance use (very zero-inflated in this sample). Thank you again for your time. |
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I think Patrick Curran has written about interactions and growth models. I don't know exact references. Aiken and West also do work with interactions. Most regression textbooks discuss interactions.
To understand what main effects mean with count variables, see:
Long, S. (1997). Regression models for categorical and limited dependent variables. Thousand Oaks: Sage.
Once you get a feeling for main effects for count variables, interactions follow. The concept of an interaction does not differ depending on the scale of the dependent variable. |
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| Nicki posted on Wednesday, May 24, 2006 - 2:47 pm
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Thank you, Linda. I have the Curran and Aiken & West references (I've done interactions in regression). I'll look at the Long one as well. I think I just need to spend some time with it re: categorical variables--somehow in the ZIP terms I get lost. I really appreciate you assuring me that the concepts are the same. Thank you,
Nicki |
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| Would it be advisable to center continuous variables before creating interaction terms for ZIP models? |
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| Yes. |
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