Table 3.
Parameter Estimates and Fit Statistics from the Unconstrained and Best-Fitting Twin Models for percent body fat.
| Standardized Parameter Estimates | Fit Statistics | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Girls | Boys | ||||||||||
| Model | A | C | E | A | C | E | −2lnL (df) | χ2(df)a | Δχ2 (df)b | p | AIC |
| Baseline | -- | -- | -- | -- | -- | -- | 1096.11 (487) | -- | -- | -- | -- |
| ACE, unconstrained | .64 (.41, .92) |
.27 (0, .50) |
.09 (.06, .13) |
.80 (.41, .87) |
0 (0, .36) |
.20 (.13, .32) |
1110.41 (499) | 14.30 (12) | -- | -- | -9.70 |
| ACE, constrained to be equal across sex | .64 (.43, .90) |
.25 (0, .46) |
.11 (.08, .14) |
.64 (.43, .90) |
.25 (0, .46) |
.11 (.08, .14) |
1140.53 (502) | 44.42 (15) | 30.12 (3) | <.01 | 14.42 |
| AE, unconstrained |
.90 (.86, .93) |
-- |
.10 (.07, .14) |
.88 (.81, .92) |
-- |
.12 (.08, .19) |
1113.80 (501) | 17.69 (14) | 3.39 (2) | .18 | −10.31 |
| CE | -- | .74 (.66, .80) |
.26 (.20, .34) |
-- | .76 (.67, .83) |
.24 (.17, .33) |
1171.12 (501) | 75.01 (14) | 60.71 (2) | <.01 | 47.01 |
| E | -- | -- | 1.0 (1.0, 1.0) |
-- | -- | 1.0 (1.0, 1.0) |
1379.30 (503) | 283.19 (16) | 269.89 (4) | <.01 | 251.19 |
Note. The unconstrained ACE model allows all genetic (A) shared environmental (C), and nonshared environmental (E) influences were allowed to vary across sex. Unless specified, models allow A, C, and E to differ across sex. Parameter estimates are standardized and range from −1.0 to 1.0. Age was regressed out of both variables prior to model fitting. The best-fitting models are indicated by boldface. Ninety-five percent confidence intervals are in parentheses. 2lnL = −2 times log likelihood of data; df = degrees of freedom; AIC = Akaike’s information criterion.
χ2 is computed by subtracting the-2lnL of the baseline model from the −2lnL of the submodel; the AIC is calculated using this fit statistic (i.e., AIC = χ2 – 2*df)
Δχ2 compares submodels to the full ACE model