Table 2.
Model results for the effects of prenatal SDP exposure on offspring substance use
| Variable | Unconditional model (UM) Estimatea [95% CI] | SDP-only model Estimatea [95% CI] | Model 1 Estimatea [95% CI] | Model 2 Estimatea [95% CI] |
| Intercept | 0.19 [0.15, 0.24]* | 0.12 [0.05, 0.18]* | 0.44 [0.05, 0.82]* | 0.15 [-0.24, 0.59] |
| SDP | ||||
| Offspring specific (OS) | – | 0.03 [0.01, 0.05]* | 0.01 [-0.02, 0.03] | – |
| Family average (FA) | – | – | – | <0.01 [-0.11, 0.10] |
| OS relative to FA | – | – | – | -0.07 [-0.18, 0.03] |
| Level 1: Covariates | ||||
| Child birth order | – | – | -0.12 [-0.22, -0.03]* | -0.13 [-0.29, 0.05] |
| Mother married | – | – | 0.02 [-0.12, 0.16] | <0.01 [-0.14, 0.13] |
| Sex (OS) | – | – | -0.04 [-0.12, 0.05] | -0.02 [-0.13, 0.09] |
| Sex (FA) | – | – | – | -0.03 [-0.15, 0.10] |
| Mother education (OS) | – | – | -0.01 [-0.04, 0.02] | <0.01 [-0.07, 0.06] |
| Mother education (FA) | – | – | – | -0.01 [-0.04, 0.02] |
| Food stamps (OS) | – | – | -0.02 [-0.18, 0.12] | 0.20 [-0.08, 0.47] |
| Food stamps (FA) | – | – | – | -0.05 [-0.24, 0.14] |
| Mother age (OS) | – | – | <0.01 [-0.01, 0.01] | -0.03 [-0.08, 0.03] |
| Mother age (FA) | – | – | – | <0.01 [-0.01, 0.01] |
| Father SDP (OS) | – | – | <0.01 [-0.03, 0.03] | 0.01 [-0.05, 0.06] |
| Father SDP (FA) | – | – | – | -0.01 [-0.05, 0.03] |
| Level 2: Covariates | ||||
| Mother substance use | – | – | 0.02 [-0.03, 0.07] | 0.01 [-0.04, 0.06] |
| Father substance use | – | – | 0.02 [-0.04, 0.08] | 0.02 [-0.04, 0.08] |
| Varianceb | ||||
| Individual-level variance | 0.14 [0.11, 0.17]* | 0.12 [0.09, 0.14]* | 0.11 [0.09, 0.14]* | 0.12 [0.10, 0.15]* |
| Family-level variance | 0.02 [<0.01, 0.05]* | 0.01 [<0.01, 0.03]* | 0.01 [<0.01, 0.04]* | 0.01 [<0.00, 0.03]* |
| Slope SDP variance | – | <0.01 [<0.01, <0.01]* | <0.01 [<0.01, <0.01]* | <0.01 [<0.01, 0.01]* |
| Intraclass correlation % within-family variance | 0.10 [0.01, 0.28]* | 0.07 [0.01, 0.25]* | 0.09 [0.01, 0.29]* | 0.04 [0.01, 0.22]* |
| explained beyond UM | – | 14% | 21% | 14% |
Notes: Covariates included in Models 1 and 2: Offspring-level covariates were child birth order, child sex, marital status, maternal education at birth of each child, whether the family was on food stamps at the time of child birth, mother age at the birth of each child, second-hand smoke exposure by the father during pregnancy; family-level covariates were maternal substance use and paternal substance use. Birth order was significantly (and negatively) correlated with age in this sample (r = -.87), which leads to a multicollinearity problem when modeling these data. Thus, birth order was included as a covariate rather than age given that (a) mothers usually smoked in the first pregnancy (64%) but not the second and (b) birth order was generally more highly associated with substance use measures than was age (Knopik et al., 2016; Marceau et al., 2016). CI = Bayesian credibility interval; SDP = smoking during pregnancy (maternal reported).
Point estimates are the median of the posterior distribution;
significance tests for variance terms are presented, but it is noted that variance estimates are bounded at zero; therefore this does not mean that each family has the same mean but, instead, indicates that the clustering of the children within families does not help explain any of the overall variability.
One tailed p < .05 (for positive estimates, p is the proportion of the posterior distribution that is below zero; for negative estimates, p is the proportion of the posterior distribution that is above zero).