Valentin posted on Tuesday, December 03, 2002 - 1:01 pm
I would like to examine the factor structure and the reliability (test-retest) of a 5-item observation scale (continuous variables)with data collected from a randomized clinical trial of Methylphenidate with ADHD children. So observation data are garthered a) before and after placebo and b) before and after ritalin
1) Could someone please help me with the proper design (CFA or something else)and the Mplus syntax to use for this purpose?
2) My sample size is rather low (N=81) and I don't know if even the SEM framework is suitable? Thanks in advance
bmuthen posted on Tuesday, December 03, 2002 - 7:48 pm
This sounds like an analysis of 2 groups (placebo/ritalin), and 2 time points (before/after), each time point having 5 variables. This is then a 2x5 = 10 variate outcome in 2 groups. I think of this as a longitudinal factor analysis model in 2 groups.
A similar setup for one group and 3 time points, adding growth modeling, is show in Example 22.4 in the Users' Guide, pp. 218-219.
With only 81 observations you can't have many parameters. Assuming measurement invariance across time, your model has for a given group 4 loadings, 5 intercepts, 2 factor variances, 1 factor covariance, and 1 factor mean (at the second time point), a total of 13 parameters. The other group is different at least wrt to the factor mean at the second time point. With proper randomization, the factor variance at the first time point should be invariant across the groups. So, your sample size might be ok. You can do Monte Carlo simulations to find out.