These results should be interpreted in the context of seven major methodological limitations. First, these twins were all white and born in Virginia. Whether these results would be replicated in other samples remains to be seen. Second, as the AIC performs well in simulations at identifying the true model,28 a variety of other fit indices for structural models have been proposed. Whereas correlated, their performance is not identical. The current version of Mx produces three additional indices: the Bayesian Information Criterion (BIC),56 the sample size adjusted BIC (aBIC)57 and the Deviance Information Criterion (DIC).58 Of all the models we examined (Table 2), the model that fits best by AIC (#19) also produced the best value for the aBIC and the DIC, and the second best-fit (by a single unit) for the BIC. Thus our conclusion that model 19 reflected the best balance of parsimony and explanatory power was not a result of idiosyncratic features of our preferred fit index—the AIC.
