

Random rate effect in nonlinear grow... 

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Hi I've fitted a logistic growth model to my data using the code below. However I'd now like to see whether the *rate* of change (i.e. the parameter 'alpha' in the model below) varies amongst participants, since that's my main reserach question. So.... is there any way of setting a parameter created in MODEL CONSTRAINT to be random? Or is there another way of doing this? cheers Chris MODEL: i1 by ANX3ANX8@1; s1 by ANX3* (L1) ANX4 (L2) ANX5 (L3) ANX6 (L4) ANX7 (L5) ANX8 (L6); i1 s1; i1 with s1; [i1* s1*]; [ANX3ANX8@0]; ANX3 ANX4 ANX5 ANX6 ANX7 ANX8 (a); MODEL CONSTRAINT: NEW(alpha lambda); L1 = 1/(1 + exp((1  lambda)*alpha)); L2 = 1/(1 + exp((2  lambda)*alpha)); L3 = 1/(1 + exp((3  lambda)*alpha)); L4 = 1/(1 + exp((4  lambda)*alpha)); L5 = 1/(1 + exp((5  lambda)*alpha)); L6 = 1/(1 + exp((6  lambda)*alpha)); 


A couple of thoughts: You can try to relate alpha to an observed variable using the Constraint= option and then express alpha as a deterministic fcn of that in Model Constraint. Or, you can use mixture modeling to give alpha a nonparametric distribution. Or, perhaps this paper about nonlinear growth using Mplus can be helpful: Grimm, K., Zhang Z., Hamagami, F. & Mazzocco, M. (2013). Modeling nonlinear change via latent change and latent acceleration frameworks: Examining velocity and acceleration of growth trajectories Multivariate Behavioral Research, DOI: 10.1080/00273171.2012.755111. download paper contact first author show abstract 

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