Table 3.
Genetic liability threshold models showing the relative contribution of genetic (A), shared environmental (C), and non-shared environmental (E) factors on developmental smoking trajectory group membership adjusted for age. The best fitting model for each categorization is indicated in italics. The best fitting model overall is indicated in bold italics.
| Models | Variance Components | Model Fit | Relative Model Fit | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| A (95% CI) | C (95% CI) | E (95% CI) | χ2 | df | p | AIC | χ2 diff | df diff | p diff | |
| 4 categories (Low, Increasing, Moderate, High) [MZ, DZ thresholds equated] | ||||||||||
| ACE | 43.8 (18.9, 71.3) | 31.2 (5.6, 52.8) | 25.0 (19.1, 32.4) | 112.500 | 31 | <.001 | 50.500 | |||
| AE | 76.5 (69.9, 81.8) | -- | 23.5 (18.2, 30.1) | 118.065 | 32 | <.001 | 54.065 | 5.565 | 1 | 0.018 |
| CE | -- | 65.4 (58.5, 71.4) | 34.6 (28.6, 41.5) | 124.737 | 32 | <.001 | 60.737 | 12.237 | 1 | <.001 |
| 3 categories (Low + Increasing, Moderate, High) [MZ, DZ thresholds equated] | ||||||||||
| ACE | 31.4 (7.0, 58.9) | 49.0 (23.3, 69.7) | 19.6 (13.9, 27.3) | 33.590 | 16 | 0.006 | 1.59 | |||
| AE | 82.2 (75.7, 87.2) | -- | 17.8 (12.8, 24.3) | 45.669 | 17 | <.001 | 11.669 | 12.079 | 1 | 0.001 |
| CE | -- | 73.6 (66.7, 79.4) | 26.4 (20.6, 33.3) | 40.035 | 17 | 0.001 | 6.035 | 6.445 | 1 | 0.011 |
| 3 categories (Low, Increasing+ Moderate, High) [MZ, DZ thresholds equated] | ||||||||||
| ACE | 46.0 (15.6, 76.4) | 25.0 (0, 50.8) | 29.0 (21.5, 38.6) | 29.128 | 16 | 0.023 | −2.872 | |||
| AE | 72.7 (64.2, 79.5) | -- | 27.4 (20.5, 35.8) | 31.89 | 17 | 0.016 | −2.11 | 2.761 | 1 | 0.097 |
| CE | -- | 60.8 (52.5, 68.0) | 39.2 (32.0, 47.5) | 38.048 | 17 | 0.002 | 4.048 | 8.92 | 1 | 0.003 |
| 3 categories (Low, Increasing, Moderate + High) [MZ, DZ thresholds free] | ||||||||||
| ACE | 33.7 (4.4, 66.2) | 42.6 (12.3, 67.6) | 23.8 (17.1, 32.5) | 89.797 | 14 | <.001 | 61.797 | |||
| AE | 78.3 (70.7, 84.3) | -- | 21.7 (15.8, 29.3) | 96.976 | 15 | <.001 | 66.976 | 7.179 | 1 | 0.007 |
| CE | -- | 69.8 (62.2, 76.2) | 30.2 (23.8, 37.8) | 94.958 | 15 | <.001 | 64.958 | 5.161 | 1 | 0.023 |
| 2 categories (Low + Increasing+ Moderate, High) [MZ, DZ thresholds equated] | ||||||||||
| ACE | 61.7 (9.4, 87.4) | 14.5 (0, 58.2) | 23.8 (12.5, 40.6) | 13.111 | 5 | 0.022 | 3.111 | |||
| AE | 77.4 (62.2, 87.9) | -- | 22.6 (12.1, 37.8) | 13.458 | 6 | 0.036 | 1.458 | 0.346 | 1 | 0.556 |
| CE | -- | 62.5 (48.0, 74.3) | 37.5 (25.7, 52.0) | 18.449 | 6 | 0.005 | 6.449 | 5.338 | 1 | 0.021 |
| 2 categories (Low, Increasing+ Moderate + High) [MZ, DZ thresholds equated] | ||||||||||
| ACE | 44.0 (0, 79.0) | 25.3 (0, 62.4) | 30.7 (20.1, 44.2) | 19.567 | 5 | 0.002 | 9.567 | |||
| AE | 71.2 (58.9, 80.9) | -- | 28.8 (19.1, 41.1) | 20.965 | 6 | 0.002 | 8.965 | 1.398 | 1 | 0.237 |
| CE | -- | 60.8 (49.4, 70.6) | 39.2 (29.4, 50.6) | 23.442 | 6 | 0.001 | 11.442 | 3.876 | 1 | 0.049 |
| 2 categories (Low + Increasing, Moderate + High) [MZ, DZ thresholds free] | ||||||||||
| ACE | 23.4 (0, 54.0) | 63.2 (34.5, 84.7) | 13.4 (7.6, 22.1) | 9.72 | 4 | 0.045 | 1.720 | |||
| AE | 88.7 (81.7, 93.5) | -- | 11.3 (6.5, 18.3) | 24.705 | 5 | <.001 | 14.705 | 14.985 | 1 | <.001 |
| CE | -- | 81.8 (74.4, 87.5) | 18.2 (12.5, 25.6) | 12.657 | 5 | 0.027 | 2.657 | 2.937 | 1 | 0.087 |
χ2=chi-square goodness of fit statistic; df=degrees of freedom; p=p value of model fit; AIC=Akaike Information Criterion; diff=difference