Hello, I'm running a latent growth curve model for a binary repeated measure with 9 data points. This model fits well when modeled as a quadratic growth curve with the variance of the quadratic slope factor=0. However, the intercept and (positive) linear slope growth factors have a negative covariance, where theory tells me that they should be positively related. Is this a possible sign of model misspecification? Any thoughts are most appreciated!
Thank you, this was very helpful and did the trick for the LCGM. However, when I run an autoregressive latent trajectory model with the same set of variables, the covariance between the intercept and slope is negative no matter where I center the time scores. Since centering yielded a positive covariance between the growth parameters in the LCGM, I'm wondering if there is something else that would need to be done with an ALT model that I'm missing? Again, I appreciate any suggestions you may have.