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I have read the chapters and papers on this site relating to growth mixture modeling and it seems appropriate to use for my data and questions. I am having a hard time understanding the example syntax in the example section and the user's guide, specifically which variables to use for u, y, x, w as shown in the examples. I have 2 questions: 1) I want to look at the relationship over time between school involvement (continuous variable measured at 3 time points) and alcohol use (semicontinuous variable measured at three time points, mostly 0s with rest skewed). I don't have any other covariates to include in this analysis. Should this be done with growth mixture modeling or as latent growth curves but only include nonzero data for alcohol use? 2) IF GMM is appropriate, where does the school involvement variable get included? It doesn't seem to fit as a w or x because there are multiple time points. Is there a chapter on this site or in a textbook that describes GMM step by step including how to do the syntax? 


I'm not sure, but it sounds as if alcohol use is your dependent variable for which you are interested in growth. And school involvement is your 'timevarying covariate". If that is correct and if there is a large percentage of zero alcohol use, there are several techniques to apply, all described in our Topics 34 and 6 handouts and videos. Many GMM papers are listed under Papers. 


what's different between latent class growth analysis and latent class growth mixture modeling?? please advise me about both model. 


LCGA does not allow withinclass variance. GMM does. See the handout and video from our Topic 6 short course on our website. 

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