I am currently examining whether language learning is correlated with inhibitory control for 2-year-old toddlers. I treated language and inhibitory control as two latent variables and there are four different measurements for each of the two latent variables. I ran the following model using lavaan, but the model ends up with a negative variance value for one of the LATENT variables SWITCH which measures Inhibitory control (of course the program sent a warning saying that some estimated ov variances are negative).
LANGUAGE=~a*WordComp + b*WordProd + c*SentComp+ d*SentProd
As you can see, the model is really not a huge one. However, I am really a novice in SEM though I have received formal statistical training with a master's degree in Biostatistics. I wonder whether I could learn from your insight about this. What could have happened so that the estimated variance is negative? Any suggestion about how to solve this problem would be appreciated.