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Does anyone have a good example (i.e., sample MPlus code) of a zeroinflated poisson model using the TWOLEVEL RANDOM command? Thanks! 


You can start with Example 9.2 and add: COUNT = y (i); and change the MODEL command as follows: MODEL: %WITHIN% s  y ON x; y#1 ON x; %BETWEEN% y s ON w xm; y WITH s; 


Thanks Linda! One more question if you don't mind. When running my ZIP model MPlus obviously creates the binary variable (mine is alc#1). I assumed, but wanted to confirm, that this alc#1 variable takes the 0s from my original count variable (alc) and gives them 0s in alc#1 and anyone that has a nonzero value on alc gets a 1 for alc#1. 


I am quoting from my ZIP post yesterday: "In the binary part Mplus does logistic regression for Prob(u#=1), where u# is a binary latent inflation variable and u#=1 indicates that the individual is unable to assume any value except 0. This is called the zero class. " So anyone who has a nonzero value on alc gets a 0 for alc#1. In other words, alc# (alc#=1) represents the inflation  the 0 part. 

Stella Resko posted on Wednesday, November 19, 2008  4:16 pm



I was wondering if anyone has a good example (i.e., sample MPlus code) of a zeroinflated poisson model that includes an interaction? Thanks! 


Do you mean interaction between 2 IVs? If so, you just use Define to create that interaction and use it as another IV. 


Hello, I was wondering if there is a limit on how many variables can be treated as count variables within a ZIP model? Can only endogenous variables be zero inflated for the model to converge? Thanks! Paige 


Q1. No Q2. Typically ZIP modeling is applied to DVs. After all, how would you formulate influence from a ZIP variable (that is, having the ZIP variable as an IV)? Treating the counts as a continuous variable would be unsatisfactory, I would think. 


Dr. Muthen, Thank you for your response! That helps. Best, Paige 

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