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Mplus Discussion > Growth Modeling of Longitudinal Data >
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 Dayuma Vargas posted on Thursday, March 29, 2012 - 2:17 am
Hello there,

I am testing a PPM. I first modeled separate LGMs for each construct and tested for gender differences in each LGM. Construct A showed a significant positive linear slope as well as a significant negative quadratic slope (I have 5 time points). Multi-group analysis of Construct A's LGM did not reveal any gender differences at this point. Similar results occurred for Construct B.

I then tested a general PPM of these constructs and found good model fit as well as significant connections between different growth parameters of the constructs. I then ran multi-group analysis to the PPM to investigate gender differences on the associations between Construct A and Construct B. Two group differences at the parameter mean level appeared: the linear and quadratic slopes for Construct A were significantly different for men and women - these parameters were significant only for men and not for women. Here is my problem: the direction of the slopes for Construct A for men in the PPM differ from the general LGM for Construct A - in the PPM, Construct A showed a significant NEGATIVE linear slope as well as a significant POSITIVE quadratic slope. The slopes for women, though non-significant in the PPM, follow the direction originally revealed in the LGM. I am not sure what this means - is my model unstable?

Thank you for any insight you may be able to provide me.
 Linda K. Muthen posted on Thursday, March 29, 2012 - 10:23 pm
What is a PPM. Are you saying that you get different results across groups for a single process when looking at it alone versus looking at it with another process?
 Dayuma Vargas posted on Tuesday, January 07, 2014 - 5:54 pm
Very very late reply, but yes, that is what I mean. Any insight? Thank you.
 Linda K. Muthen posted on Tuesday, January 07, 2014 - 6:26 pm
Please send the relevant outputs and your license number to support@statmodel.com.
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