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I am interested in a fitting a model with a count outcome using a zerotruncated poisson model. The following discussion board postings seem to indicate that zerotruncated poisson is available:  http://www.statmodel.com/discussion/messages/11/2675.html?1318823019 (see the Oct 16, 2011 posting by Bengt Muthen)  http://www.statmodel.com/discussion/messages/23/6763.html?1311444916 (see the Feb 17, 2011 posting by Bengt Muthen as well as the July 23, 2011) However, I've looked through the user manual and it doesn't seem to be an option. The truncated negativebinomial seems to the only option available for a zerotruncated count model. Is that correct? Have I overlooked something? I'm using Mplus 6.12. Thanks for your help. Best, Scott 


I agree that the only zerotruncated model is the zerotruncated negative binomial model. 


You can fix the alpha dispersion parameter of negbin to a small value to approximate Poisson. Like 0.01. 

Daniel Lee posted on Thursday, March 12, 2020  7:48 am



Hi Dr. Muthen, I ran a zerotruncated negative binomial model. I am trying to get incident rate ratios (IRRs). Is it OK to run the following model constraint command to obtain these rates (by exponentiating the coefficients): model constraint: new(b1_exp b2_exp b3_exp); b1_exp = exp(a1); b2_exp = exp(a2); b3_exp = exp(a3); 


Yes, that's how you do it. 

Daniel Lee posted on Friday, March 13, 2020  10:59 am



I own a copy of the regression and mediation analysis using Mplus book. While there is some mention of the zerotruncated negative binomial model, it is within the context of a tworegression hurdle model. Does the analysis become a zerotruncated negative binomial regression, if in table 6.5 (page 270), I remove the following code from Model command (while keeping "naffairs ON kidsyrsmarr6"): naffairs#1 ON kidsyrsmarr6; 


No, you should instead look at Table 6.7 in our book and the text on page 272 that goes with it. 

Daniel Lee posted on Saturday, March 14, 2020  7:38 pm



Hi Dr. Muthen, In page 272, a hurdle model was estimated that specifies one process for zero counts and another process for positive counts. In my data, the value zero cannot occur. Hence, I thought that the following syntax would be correct: Usevariable: Names = y x1 x2; Usevar = y x1 x2; Count = y(NBH); Model: y ON x1 x2; Analysis: Estimator=MLR; Relative to Table 6.7, I removed the following code (y#1 on x1 x2) because this specifies a logistic regression for the binary outcome being greater than zero. Please let me know if I am interpreting/comprehending something incorrectly in the book. Again, I very much appreciate your help. Thank you. 


You should use the NBT option and say: Usevariable: Names = y x1 x2; Usevar = y x1 x2; Count = y(NBT); Model: y ON x1 x2; Analysis: Estimator=MLR; 

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