I would like to estimate a Multiple Cohort Growth Model similar to the example in ch 6.18 of the user guide. Instead of cohorts based on birth year, my three cohorts are grouped according to grade at baseline – 3rd, 6th, and 9th grade.
So ages within each cohort do range at each assessment (each cohort was assessed at three timepoints – 18 months apart). Can I use the syntax from 6.18 as-is or are there any adjustments I need to make to how my data is structured or to the syntax?
Below is a draft of my syntax, thanks! Note: APD is the outcome whose trajectory I want to model.
GROUPING = g (1 = 3RD 2 = 6TH 3 = 9TH ); MODEL: i s |APD1@0APD2@.15APD3@.3; [i] (1); [s] (2); i (3); s (4); i WITH s (5); APD1 ON age1; APD2 ON age2; APD3 ON age3 (g6); APD1-APD2; APD3 (v6); MODEL SIXTH: i s |y1@.3y2@.45y3@.6; APD1 ON age1 (g6); APD2 ON age2; APD3 ON age3 (g9); APD1 (v6); APD2; APD3 (v9); MODEL NINTH: i s |y1@.6y2@.75y3@.9; APD1 ON age1 (g9); APD2 ON age2; APD3 ON age3; APD1 (v9); APD2-APD3;
using the same basic model design above, I have moved on to using multiple indicators for the outcome at each timepoint.
So APD1, APD2, and APD3 are now latent factors made up of two manifest indicators each (e.g., APD1 BY apd_c apd_p).
The model runs ok except that the mean for the intercept growth factor of my first group (Grade 3) is zero. This does not fit well with my data. I would like to free it to vary but nothing I have tried works - using an *, setting a starting value, labeling it. Can you help?