Hi all,
I have a question about bivariate cholesky ACE model. For model fitting, I compared the reduced models (selectively dropping a21, c21 and e21) to the full bivariate ACE model and the best-fitting model was selected based on lowest AIC and nonsignificant likelihood ratio chi-square test.
However, I noticed that the best-fitting model’s ACE estimates do not seem to match with what I obtained from fitting each of the two variables in univariate ACE models. For example, in univariate model fitting I got:
First trait: C = 60% (CI: 0.46-0.71) and E = 40% (CI: 0.29-0.54).
(Full ACE model: A = 5% (CI: NA-0.60), C = 55% (CI: 0.04-0.71), E = 39% (CI: 0.27-0.54))
Second trait: A = 82.6% (CI: 0.74-0.88) and E = 17.4% (CI: 0.12-0.26)
(Full ACE model: A = 72.4% (CI: 0.31-0.88), C = 10% (CI: 0-0.51), E = 17.4% (CI: 0.12-0.26))
The best fitting bivariate model for the two traits is ACE (drop c21 and e21) and the estimates are as follows:
confidence intervals:
lbound estimate ubound note
ACEnce21.SA[1,1] 1.261549e-01 0.2769508 0.6573700
ACEnce21.SA[2,2] 3.757661e-01 0.7011000 0.8840258
ACEnce21.SC[1,1] 3.156919e-02 0.3914759 0.5619521
ACEnce21.SC[2,2] 1.939172e-42 0.1306183 0.4428392
ACEnce21.SE[1,1] 2.354506e-01 0.3315733 0.4584370
ACEnce21.SE[2,2] 1.133622e-01 0.1682817 0.2513258
ACEnce21.rA[2,1] NA -1.0000000 -0.6036494 !!!
ACEnce21.corrA[1,1] -5.549520e-01 -0.4406475 -0.3113180
(Full BivACE model)
confidence intervals:
lbound estimate ubound note
BivACE.SA[1,1] 1.669727e-03 0.17771597 0.68945684
BivACE.SA[2,2] 2.799714e-01 0.66712995 0.88409716
BivACE.SC[1,1] 2.803414e-03 0.48075051 0.69603875
BivACE.SC[2,2] 2.393405e-43 0.16523408 0.54170390
BivACE.SE[1,1] 2.416883e-01 0.34153352 0.47200335
BivACE.SE[2,2] 1.122780e-01 0.16763597 0.25194368
BivACE.rA[2,1] NA -1.00000000 -0.99750231 !!!
BivACE.rC[2,1] -1.000000e+00 -0.24981942 1.00000000
BivACE.rE[2,1] -4.071271e-01 -0.17633429 0.06402325
BivACE.corrA[1,1] -6.319900e-01 -0.34432491 -0.02917323
BivACE.corrC[1,1] -3.865143e-01 -0.07041025 0.20042770
BivACE.corrE[1,1] -1.118121e-01 -0.04219267 0.01531362
As can be seen, the bivariate ACE estimates are rather different for trait 1 especially. In view of this, should I trust the ACE estimates yielded by the univariate ACE modelling more than the ones obtained from bivariate ACE modelling?
Besides that, the rA (genetic correlation) between the two traits appear to be -100%, which seems quite drastic. Can I actually put much weight on the results and interpret the findings accordingly?
Will greatly appreciate the input from the various OpenMx experts on this forum.