Table 2.
Model-fitting Results
Model Comparison | Hypothesis | Overall Fit | Fit of Nested Model | |||||
---|---|---|---|---|---|---|---|---|
Log-likelihood | df | χ2 | p | Δχ2 | Δdf | Δp | ||
1 | None: Saturated model | −17584.4 | 0 | |||||
2 vs. 1 | Latent growth model conforms to the dataa | −17590.4 | 8 | 12.0 | .15 | |||
3 vs. 2 | Linear growth in males, i.e., middle time point = 0.5 | −17598.1 | 12 | 27.4 | .01 | 15.4 | 4 | < .01 |
4 vs 2 | Linear growth in females, i.e., middle time point = 0.5 | −17630.3 | 12 | 91.8 | < .01 | 79.8 | 4 | < .01 |
5 vs. 2 | Nonlinear growth, i.e., fixed time point at .53 in males and .63 in females | −17593.3 | 16 | 17.9 | .33 | 5.8 | 8 | .67 |
6 vs 5 | Equal parameters across co-twins and zygosity groups | −17627.3 | 68 | 85.9 | .07 | 68.0 | 52 | .07 |
7 vs 6 | No intercept-slope correlation | −17628.9 | 74 | 89.0 | .11 | 3.2 | 6 | .78 |
8 vs 7 | Intercept mean is equal between males and females | −17644.8 | 75 | 120.9 | < .01 | 31.8 | 1 | < .01 |
9 vs 7 | Intercept variance is equal between males and females | −17645.8 | 75 | 122.8 | < .01 | 33.8 | 1 | < .01 |
Notes. Overall fit is in reference to the saturated model. Likelihood ratio test is based on twice the difference in log-likelihood values between nested models, which is distributed as chi-square; df = degrees of freedom.
Middle time point was freely estimated in all groups.