Table 3.
Results of Selected Phenotypic Models of Anxiety Trajectory over Age, Based on 5091 observations from 1482 twins aged 50 and older.
| (a) No Age Change | (b) Linear Age | (c) Quadratic Age | (d) Cubic Age | |||||
|---|---|---|---|---|---|---|---|---|
| B | SE | B | SE | B | SE | B | SE | |
| Fixed Effects: | ||||||||
| Intercept | 17.72 | 0.30 | 17.68 | 0.30 | 17.53 | 0.32 | 17.59 | 0.33 |
| Female (1=Y, 0=N) | 1.92 | 0.39 | 1.91 | 0.39 | 1.78 | 0.39 | 1.80 | 0.39 |
| Mode (1=IPT, 0=Q) | −0.67 | 0.20 | −0.70 | 0.21 | −0.65 | 0.20 | −0.64 | 0.20 |
| Birth year | −0.05 | 0.02 | −0.04 | 0.03 | −0.02 | 0.03 | −0.05 | 0.04 |
| Die ≤ 2 yrs (1=Y, 0=N) | −0.38 | 0.60 | −0.47 | 0.61 | −0.69 | 0.61 | −0.74 | 0.61 |
| Female * Die ≤ 2 yrs | 2.02 | 0.92 | 2.03 | 0.93 | 1.98 | 0.93 | 2.16 | 0.93 |
| Age | -- | -- | 0.01 | 0.03 | 0.01 | 0.03 | 0.03 | 0.04 |
| Age2 | -- | -- | -- | -- | 0.003 | 0.001 | 0.01 | 0.003 |
| Age3 | -- | -- | -- | -- | -- | -- | −0.0003 | 0.0001 |
| Age * Birth year | -- | -- | -- | -- | 0.01 | 0.005 | ||
|
| ||||||||
| Random Effects: | ||||||||
| Level 3 (Between-Pair): | ||||||||
| Intercept | 11.36 | 1.97 | 11.01 | 1.95 | 11.24 | 1.98 | 11.05 | 1.97 |
| Level 2 (Within-Pair): | ||||||||
| Intercept | 23.43 | 1.95 | 21.97 | 2.07 | 27.19 | 2.46 | 27.25 | 2.47 |
| Linear slope | -- | -- | 0.19 | 0.10 | 0.02 | 0.14 | 0.03 | 0.14 |
| Quadratic slope | -- | -- | -- | -- | 0.10 | 0.02 | 0.10 | 0.02 |
| Intercept-linear slope covariance | -- | -- | −0.14 | 0.10 | 0.14 | 0.14 | 0.12 | 0.14 |
| Intercept-quadratic slope covariance | -- | -- | -- | -- | −0.10 | 0.02 | −0.10 | 0.02 |
| Linear-quadratic slope covariance | -- | -- | -- | -- | −0.002 | 0.001 | − 0.002 | 0.001 |
| Level 1 (Within-Person, Across-Time) | ||||||||
| Residual | 24.99 | 0.59 | 24.24 | 0.61 | 22.27 | 0.61 | 22.26 | 0.61 |
|
| ||||||||
| Model Fit Compared to Baseline†: | ||||||||
| Δ−2LL (Δ parameters) | −51.7 | (+5) | −66.1 | (+8) | −124.3 | (+12) | −137.3 | (+14) |
| ΔAIC | −41.7 | −50.1 | −100.3 | −109.3 | ||||
| ΔBIC | −17.3 | −11.1 | −41.7 | −41.0 | ||||
Note: Bold indicates p ≤.05. Italics indicates p ≤.10. −2LL = −2 log-likelihood; df = degrees of freedom. Age was centered at 67; birth year was centered at 1920.
†
Model fit was compared against a baseline model with a fixed intercept and random intercepts at L2 and L3 (−2LL = 33287.9 for 4 parameters, AIC = 33295.9, BIC = 33315.4).