Syntax for modeling "holiday effects"... PreviousNext
Mplus Discussion > Growth Modeling of Longitudinal Data >
 Jen posted on Wednesday, June 01, 2011 - 7:10 am

I have read several of the papers that model non-linear "holiday effects" in longitudinal data with many waves. This makes sense to me conceptually, but I wanted to make sure I understood the proper syntax.

I am 8 waves of drinking data, and there seems to be a large dip in drinking for two months in the midst of winter, meaning the data is not fit well by a linear or quadratic model alone.

If I want to model this drop, is the following syntax correct?

ibinge sbinge qbinge | binge2@0 binge3@1 binge4@2 binge5@3 binge6@4 binge7@5 binge8@6 binge9@7;

ibinge winter | binge2@0 binge3@0 binge4@0 binge5@0 binge6@0 binge7@1 binge8@1 binge9@0;

(7 & 8 are the months with the drop)

This model seems to fit the data well, and there is variation in all parameters that could then be predicted by covariates...

 Linda K. Muthen posted on Wednesday, June 01, 2011 - 10:35 am
I would do this using an intercept only model to take the drop into account, for example,

winter | binge7 binge8;
 Jen posted on Wednesday, June 01, 2011 - 12:32 pm
Thank you! That seems to work well.
 Jen posted on Thursday, June 09, 2011 - 11:47 am
One more quick question related to this -- if I am interested in modeling an effect like this that occurs at only one time point (e.g., just binge7) or at multiple, non-consecutive time points (e.g., binge3 and binge7), what would be the best syntax for that? I've noticed that the intercept only model causes some issues, even if I hold the variance at 0 for winter (and there is a lot of variance in winter when 7 & 8 are included, so the 0 variance model probably isn't the best)...

Thanks for any advice!
 Linda K. Muthen posted on Thursday, June 09, 2011 - 2:13 pm
Perhaps the following paper that is on the website will help:

Greenbaum, P.E., Del Boca, F.K., Darkes, J., Wang, C. & Goldman, M.S. (2005). Variation in the drinking trajectories of freshman college students. Journal of Consulting and Clinical Psychology, 73, 229-238
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