Table 4.
Model fit summaries of multivariate ACE and independent pathway models: HCP data. Models tested to identify genetic relationship between subfields in the VETSA sample. For omnibus tests of a given variance component (A, C, or E), the covariance (but not variance) was constrained to zero while the covariance of the remaining variance components was estimated freely. The independent pathways section presents results of the model identification procedure. All models except the one‐factor model provided a good fit relative to the ACE Cholesky. While there was no significant reduction in fit between the four‐ and three‐factor models, the comparison of the three‐ versus two‐factor models resulted in a significant reduction in fit, indicating that the three‐factor solution provided the best model for further testing
| Model | Estimated parameters | −2LL | df | ΔLL | Δdf | p |
|---|---|---|---|---|---|---|
| Omnibus tests of covariance | ||||||
| ACE Cholesky | 246 | 8,635.54 | 6,426 | – | – | – |
| ACE no A covariance | 180 | 8,824.25 | 6,492 | 188.71 | 66 | 0 |
| ACE no C covariance | 180 | 8,669.35 | 6,492 | 33.81 | 66 | 1 |
| ACE no E covariance | 180 | 11,299.3 | 6,492 | 2,663.75 | 66 | 0 |
| Independent pathway models of A | ||||||
| ACE Cholesky | 246 | 8,635.54 | 6,426 | – | – | |
| Ind. path. A six factors | 243 | 8,638.17 | 6,435 | 2.63 | 9 | 0.98 |
| Ind. path. A five factors | 235 | 8,641.62 | 6,442 | 6.07 | 16 | 0.99 |
| Ind. path. A four factors | 226 | 8,651.69 | 6,450 | 16.15 | 24 | 0.88 |
| Ind. path. A three factors | 213 | 8,666.11 | 6,459 | 30.57 | 33 | 0.59 |
| Ind. path. A two factors | 205 | 8,687.65 | 6,469 | 52.11 | 43 | 0.16 |
| Ind. path. A one factor | 193 | 8,717.5 | 6,480 | 81.96 | 54 | 0.01 |
| Independent pathway models of A (three vs. two factors) | ||||||
| Ind. path. A three factors | 213 | 8,666.11 | 6,459 | – | – | – |
| Ind. path. A two factors | 205 | 8,687.65 | 6,469 | 21.55 | 10 | 0.02 |
−2LL = −2 log‐likelihood; df = degrees of freedom; HCP = Human Connectome Project; LRT = likelihood‐ratio chi‐square test; p = significance of the LRT; VETSA = Vietnam Era Twin Study of Aging.