I use a set of about 20 attitudinal items and confirmatory factor analysis (CFA). Loadings and model for are sufficient. In the next step, I want to test for correlations between these latent factors. I calculate factor scores based on the CFA. And here comes my question: If I calculate correlations between these factor scores, correlations are quite high (up to .7). If I calculate sum scores (adding up the items) and correlate these scores I get only a medium correlation. How does this come? I am aware that the latent factor in the CFA are weighted while the sum scores are not. However, I do not think that this can be the reason for the different correlations.
General framework: N > 8000, Likert scale, attitude items.
This is a similar topic, but does not on the possible differences between the two methods. Correlational study or ordinal data using 5-point Likert scale
edited to make the question more clear