We estimated all models in Mplus [36] using a weighted least squares estimator with theta parameterization. We used clustering (based on family membership) to account for the non-independence of the twin observations within the MTFS sample. We considered absolute model fit in terms of RMSEA (with values less than 0.06 indicating a well-fitting model), as well as CFI and TLI (with values greater than 0.95 indicating a well-fitting model [37]). We evaluated relative model fit by the difference in CFI values. If the difference in CFI values between constrained and unconstrained models was less than 0.01, or if the fit indices were substantially better in the simpler constrained model, we retain the null hypothesis that the factor structure is the same between groups. [38]
