Monday, July 15, 2013

We sketch here some practical guidelines on how to:
1. Run a paired t-test to answer the question: 'Did outcome Y change from baseline to follow-up" - in AMOS v. 5 [free software, this version only] and in Mplus.
2. Compare the paired t-test results to a flexible model where the change is allowed to depend on the initial values of Y (which the paired t-test does not allow).
3. Compute statistical power for the 2 models, and see which fares best, and why; this can be easily done with very simple syntax ran in Mplus.
For more detailed input and output files to replicate all our analyses, go to: 
The changes seem dramatic when outcomes are not centered [see last image below], less impressive when wave 1 and wave 2 measures are centered on the wave 1 mean [right below], still some differences are notable, see 2nd graph of p values.

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