Help with longitudinal, overdispersed, count data via PROC GLIMMIX

PSB — Fri, 04 Feb 2022 17:34:57 GMT

Hi all,

I'm relatively new to the world of SAS - I have some experience running PROC MIXED but have not needed to use SAS all too much throughout my graduate training. Here's a summary of my data that is being used for my dissertation:

- Approximately 50 youth, diagnosed with certain mental health disorders, who were a part of an intensive, 5-week treatment program

- The outcome of interest is aggression which is a continuous, non-negative, count variable and is showing a negative binomial distribution (highly positively skewed with var > mean). This outcome was measured across the 5 weeks - thus, each child has a weekly aggression score

- This outcome is showing a highly skewed distribution across the 5 weeks

- I am interested in whether certain pre-treatment affective states (e.g., irritability) predict changes in the intercept and slope/trajectory of aggression across the 5 treatment weeks

- Importantly, treatment did NOT differ across youth; they all received the same treatment

The various resources I have read online suggest PROC GLIMMIX to be the ideal approach but the issue I am running into is that every single resource/example implies that GLIMMIX is best suited for clustered data where participants are separated into various conditions. Again, that is not the case for my data. I have scores nested within youth but that is it.

I've consulted various resources and have piecemealed syntax that runs a converging model without errors (all predictors have been centered hence the 'c'):

PROC GLIMMIX DATA = diss.stplong method=quad;
Class STPID;
Model CPsum = cirr clpe cweek / s link=log dist=negbin;
Random intercept / sub = STPID;
Run;

I removed the random effect of week from the RANDOM statement as that led to the estimated G matrix being not positive definite. I'd appreciate any/all feedback. Apologies for the long post and sorry for any elementary mistakes I've made in this.

Thanks so much.

-Pev.

Re: Help with longitudinal, overdispersed, count data via PROC GLIMMIX

Ksharp — Sat, 05 Feb 2022 08:00:19 GMT

You are better post it at Stat Forum.

https://communities.sas.com/t5/Statistical-Procedures/bd-p/statistical_procedures

and calling @StatDave @SteveDenham @lvm

topic Help with longitudinal, overdispersed, count data via PROC GLIMMIX in SAS Programming

Help with longitudinal, overdispersed, count data via PROC GLIMMIX

Re: Help with longitudinal, overdispersed, count data via PROC GLIMMIX