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Please excuse me if this has been answered already, but I couldn't tell from the threads. We want to use ZINB because we have a highly nonnormal count distribution (of mental health visits) with a very large number of 0's and standard deviation much larger than the mean. We believe that ZINB is the best way to handle this. Does Mplus version 5.2 cover this analysis? Thank you very much! VAguy 


Yes, this model can be estimated in Mplus. It was added in Version 5.1. See the Version 5.1 Language Addendum and the Version 5.1 Examples Addendum which are on the website with the user's guide. 


See also the 4th (bottom) web talk at http://www.statmodel.com/webtalks.shtml which goes through an example in Hilbe's negative binomial book. 


Thank you both for your responses! I will review these this week! ~mag 

LAS posted on Tuesday, September 28, 2010  12:28 pm



Hello. I am currently running LCGA and GMM models using highly skewed data with a large percentage of 0s. I explored using four different models: the Poisson, Zeroinflated Poisson (ZIP), negative binomial, and Zeroinflated Negative Binomial (ZINB). Compared to the NB and ZINB, the Poisson and ZIP performed poorly (based on the BICs), so I eliminated these models from consideration. When I ran the ZINB, mplus set the logit parameters for all classes to 15 (regardless of how many classes I extracted). As a result, the ZINB seemed to reduce to the NB with the ZINB and the NB producing identical log likelihoods. Based on these results, can I assume that the inflation parameters are not needed and that the most appropriate model is the NB? Thank you! 


Yes. I assume you have multiple classes as well. That sometimes removes the need for zeroinflation, at least for NB which already picks up the preponderance of zeros to some extent  at least better than Poisson. 


Hi A question on missing values. Are they also handled via FIML for ZINB ZIP or inflated hurdle models in Mplus? Can i argue in a paper that this is possiple because all the mentioned modells are calculated using ML estimator which is the basis also for fiml? Thanks 


I don't think of FIML as being in operation when you have only a single dependent variable as you do in those regression models. Dealing with missing on the DV is simply the same as deleting the subject because it has no information on the relationship between the DV and covariates, nor on the DV. Dealing with missing on covariates goes beyond the regression model. For FIML  that is ML under MAR  to play a role you need more than one DV so that missing on one of them borrows information from the other. 


I am running a zeroinflated Poisson LCA model with three count outcomes that measure the number of days of prescription drug use (stimulants, pain killers, and sedatives) in the prior 3 months. I have three questions regarding this analysis: 1. If I have a variable that could indicate true structural zeros (i.e., we measured whether or not participants had ever used each class of drugs in their lives), would it be better to include those as class indicators than to run a zeroinflated model? 2. Can you briefly explain the difference between the default of fixing the inflation parameters across classes versus freeing them? I'm having trouble finding a reference that would assist me in the relative interpretation of the two. 3. The model is giving me a message under the model fit section saying "** Large values were truncated at 9." Does this mean that the analysis truncates all values (which range all the way to a value of 90) to 9 for the purpose of analysis, or just for the purpose of computing chisquare statistics? Can you point me to any references on the appropriateness and interpretability of this and how this affects the sample and estimated means for the count variables? Thanks in advance for your help! 


1. You can create a zero class using it as separate group by Knownclass, where that group has zero prob of Y>0. But it may just complicate matters  I would stick with last month reports. 2. I would let them be different across classes  a high class for instance may have less inflation than a low class. Maybe the 1989 Roeder et al JASA article talks about this. 3. That refers only to the chi2 testing, not the subsequent analysis. 


I would like to use zeroinflated negative binomial regression, but could find syntax only for ZIP  COUNT IS u1(i)  and NB  COUNT IS u1(nb) in Version 7 Mplus User's Guide. What should I use for ZINB instead of "nb"? 


Never mind. Just found that it was nbi. Sorry about that. 


Good. 

Amy Hoffmann posted on Thursday, September 22, 2016  7:17 am



Hello Drs. Muthen, I am running analyses using ZINB models to examine gender interactions in a set of variables in the count model. In the zero model, I put three variables that would be theoretically associated with production of excess zeroes. When I ran the model using the full sample, everything ran fine and there was a significant gender interaction in the count model. I then split the sample by gender and ran similar models in each sample. This model ran fine in the female sample, but is producing the following error in the male sample: ONE OR MORE PARAMETERS WERE FIXED TO AVOID SINGULARITY OF THE INFORMATION MATRIX. THE SINGULARITY IS MOST LIKELY DUE TO THE MODEL IS NOT IDENTIFIED, OR DUE TO A LARGE OR A SMALL PARAMETER ON THE LOGIT SCALE. THE FOLLOWING PARAMETERS WERE FIXED: Parameter 5, TOTALPERP#1 ON INP_NUM Parameter 3, TOTALPERP#1 ON INC_NUM Parameter 4, TOTALPERP#1 ON AGE Parameter 1, [ TOTALPERP#1 ] While it produced normal looking output in the count model, it's not giving me values for standard error or p in the zero model. Everything I've found seems to suggest that there may be a problem with restricted variance in the fixed variables, but I don't think that's the case here, as the distributions are similar for males and females. Any thoughts you have would be greatly appreciated. Thanks, Amy 


Perhaps males don't need the zeroinflation. Check using BIC. You can also run without covariates and see of the inflation intercept gets close to 15, indicating that the inflation part is not needed. 

Amy Hoffmann posted on Thursday, September 22, 2016  1:31 pm



Hello Dr. Muthen, Thank you for the prompt reply. I ran the model as a regular negative binomial, and the BIC increased significantly from the ZINB model (going from 702.424 to 724.688), indicating the ZINB is a better fit. What do you mean by run without the covariates? Thanks again for your help. 


So instead of saying y on x; you say y; If this doesn't help, we need to see your input, output, data  send to Support along with your license number. 

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