GMM for non-normal ordinal outcome PreviousNext
Mplus Discussion > Growth Modeling of Longitudinal Data >
 jhodel posted on Thursday, October 03, 2019 - 6:39 am
Dear all,
I would like to perform GMM on longitudinal data about persons undergoing clinical rehabilitation in order to explore the number of classes of recovery during rehabilitation. The study design includes max. 4 repeated unstructured measurement time points of an ordinal outcome (sum score between 0 and 100) which is non-normally distributed.
Therefore I was thinking of fitting a skew-t GMM for categorical outcomes with individually-varying time scores. Is this possible in Mplus and do you have any examples on this?

I also read into the R package lcmm, which seem to be able to perform the desired GMM with unstructured data, non-normal and ordinal outcome by using Link Functions and Latent Process Mixed Models ( Unfortunately, there is very few literature around which describes the differences between the approaches used in the lcmm package and Mplus for skewed and categorical outcomes. Therefore, I was wondering if you know more about the differences and advantages/disadvantages of the two approaches used in these two softwares?

Thanks a lot in advance! Best regards,
 Bengt O. Muthen posted on Thursday, October 03, 2019 - 2:33 pm
Skew-t GMM works well with skewed variables where the cause for the skewness is NOT strong floor or ceiling effects. See e.g.

Muthén, B. & Asparouhov T. (2015). Growth mixture modeling with non-normal distributions. Statistics in Medicine, 34:6, 1041–1058. DOI: 10.1002/sim6388

I will send you an output from this.

I am not sure you need to treat your outcome as ordinal - it sounds sufficiently interval scaled to be considered a continuous variable.

I am not familiar with lcmm but it probably does something similar. You can try it and compare - check that you have the same number of parameters and best loglikelihood value.
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