Proc Traj for data with negative binomial distribution

[agnesyyf]

Dear all SAS experts,

My dataset is a longitudinal one, comprising 7 time points; for each time point, we count the number of online posts under certain topics for 800 users. I intend to discover whether there are different patterns of change in the number of posts across the 7 time points among these users. so, this will be an LCGA (Latent Class Growth Analysis) or GBTM (Group-Based Trajectory Modeling). 

Exploratory analysis found that our data are overdispersed (variance>>mean) and contained excess zero, and it fit negative binomial (NB) or zero-inflated negative binomial (ZINB) distribution better (preliminary analysis using MPLUS showed that NB and ZINB perform similarly, and both are better than ZIP). For the ease of handling time-varying covariate, I would like to use Proc Traj for GBTM. However, Proc Traj does not support an NB/ZINB model.

So, I wonder if there are any ideas on how I can handle my NB data using Proc Traj? I found that some studies used ZIP as an alternative for ZINB (see https://journals.sagepub.com/doi/10.1177/154405910808700112), is this appropriate? 

Thanks for your answer in advance!

[sbxkoenk]

Hello,

I guess you know this , but just to be sure …

You CANNOT contact SAS Technical Support regarding your question on PROC TRAJ.
But, of course, you CAN post your question into the SAS Communities and that's what you have done. I hope other PROC TRAJ users can help you out. You can search the SAS Communities for similar or other PROC TRAJ questions.

PROC TRAJ is not a procedure developed, distributed, or supported by SAS Institute.  It is a user-written procedure available from a third party.  When asked about PROC TRAJ, SAS recommends customers do an internet search for it.  For questions, customers need to contact the author of that procedure directly for assistance.  
The PROC TRAJ web page is :

   http://www.andrew.cmu.edu/user/bjones/

SAS does not have a procedure that is an alternative for PROC TRAJ at this moment.

BR,

Koen