Re: Plotting Interaction from Zero-inflated Poisson Regression

Posted by Ryan on Feb 05, 2011; 3:52am
URL: http://spssx-discussion.165.s1.nabble.com/Is-there-a-way-to-get-eigenvalues-from-CATPCA-tp3370023p3372193.html

Dale,

 

I'm confused by your post. First you state that you fit a zero-inflated poisson (ZIP) model in MPLUS, presumably because you have count data with excess zeros, but you then reportedly fit a Poisson model on the same data in SPSS to obtain predicted values. Which model yields a superior fit? (You could construct a likelihood ratio test to compare overall fit of each model.) If the ZIP model is superior, then that is the model from which you should obtain predicted values.

 

Ryan

 

On Thu, Feb 3, 2011 at 7:26 PM, Dale Glaser <[hidden email]> wrote:

Hi all......I have ran a multiplicative model (group x test score) using zero-inflated Poisson (ZIP) in Mplus given the DV (# of fails). The interaction term is significant for the Poisson component of the model, and now we are trying to plot the interaction  This is where I am stuck.  I couldn't find a way by which to graph this result via Mplus so I used the GENLIN option in SPSS with the log link function for the Poisson model, and thought if I saved the predicted scores I could plot the two groups x moderator interaction (as you can with OLS regression when you graph a scatterplot of the moderator and outcome and use the subgroup fit line option to super-impose the predicted lines for each group).  However, as most of you would expect when I graph the predicted scores from GENLIN against the moderator and plot the two group fit lines, it only shows the two lines since it is a perfect fit for each group.  So, does anyone have any suggestions how to overlay the predicted line for subgroups over the scatterplot based on the results from a Poisson model?   thank you very much....dale   Dale Glaser, Ph.D. Principal--Glaser Consulting Lecturer/Adjunct Faculty--SDSU/USD/Alliant Past-President, San Diego Chapter of American Statistical Association 3115 4th Avenue San Diego, CA 92103 phone: [phone] fax: [phone] email: [hidden email] website: www.glaserconsult.com