4.1 Descriptive Statistics
Descriptive statistics and bivariate correlations for observed predictor and control variables are presented in . While nearly half of the boys in the study endorsed a prior history of alcohol use at the initial assessment in early adolescence (46%), relatively few endorsed ever experiencing problems as the result of their use (5%). All measures of early adolescent psychopathology were positively intercorrelated. As expected, the highest correlations were between the externalizing variables of CD and ADHD symptoms, and the internalizing variables of depression and anxiety/withdrawal. Participants with higher CD symptoms were significantly more likely to report a prior history of alcohol use and alcohol use problems, as well as have a biological parent with a history of alcohol/drug problems. Higher levels of depression were also related to an increased probability of reporting prior alcohol use problems.
Descriptive Statistics and Correlations for Potential Confounds and Primary Predictor Variables
The proportion of boys who met criteria for a diagnosis of alcohol abuse without dependence and alcohol dependence by young adulthood was similar. Specifically, 21.3% of participants met criteria for alcohol abuse without dependence and 24.5% met criteria for lifetime alcohol dependence. The mean number of alcohol use disorder symptoms reported for the entire sample was relatively low (M = 2.19, SD = 2.56, Range 0 – 11), with the modal response being zero (35.6%).
4.2 Alcohol Use Disorders Symptoms
Results from the ZIP regression using early adolescent psychopathology to predict AUD symptoms are presented in . The significant predictors for the zero-inflated portion of the model included minority status and participant's prior alcohol use. Specifically, boys who reported prior alcohol use at the first follow-up and Caucasian participants were less likely to belong to the latent group of participants who were unable to assume non-zero symptoms scores (e.g., abstainers). Early adolescent psychopathology did not significantly predict the inflation portion of the AUD symptom model.
Zero-Inflated Poisson Regression Using Early Adolescent Psychopathology to Predict Lifetime Alcohol Use Disorder Symptoms by Young Adulthood.
In contrast, facets of early adolescent psychopathology were significantly related to an increased number of AUD symptoms for the count portion of the ZIP regression. After controlling for potential confounds and the overlap between measures of early adolescent psychopathology, higher levels of anxiety/withdrawal were inversely related to AUD symptoms. On the other hand, higher levels of CD symptoms were significantly related to higher levels of AUD symptoms. There were no main effects for ADHD symptoms or depression in predicting AUD symptoms.
In the second step of the regression, there was a statistically significant interaction between conduct problems and depression in predicting the number of AUD symptoms by early adulthood. As previously mentioned, recommended procedures for probing continuous variable interactions at mean levels of all other covariates in the model were used to elucidate the nature of this relation (Aiken & West, 1991
). The results from these analyses are visually depicted in . Depressive symptoms were not significantly related to AUD symptoms for participants with low (incident rate ratio (IRR) = .952, 95% confidence interval (CI) = .826 − 1.10, z
= −.671, p
= .502) and moderate (IRR = 1.038, 95% CI = .931 − 1.156, z
= .664, p
=.507) levels of CD symptoms. However, increased depression was associated with a greater number of AUD symptoms for individuals with high levels of CD symptoms at a marginal level of statistical significance (IRR = 1.131, 95% CI = .996 − 1.284, z
= 1.898, p
= .058). Overall, the results suggest that the co-occurrence of high levels of depression and CD symptoms seems to place adolescents at particular risk of developing increased AUD symptoms by young adulthood.
Interaction between conduct disorder symptoms and depression in predicting alcohol use disorder symptoms by young adulthood. Predicted values are based on the log of the incident rate ratio.
4.3 Alcohol Use Disorder Diagnoses
Multinomial regression results predicting AUD diagnoses from early adolescent psychopathology are presented in Table 4. Results indicated that early adolescent psychopathology did not significantly differentiate individuals with a lifetime diagnosis of alcohol abuse without dependence from those who never developed an AUD. In contrast, participants with higher levels of CD symptoms and lower levels of anxiety/withdrawal in early adolescence were more likely to develop a lifetime diagnosis of alcohol dependence in comparison to individuals who never developed an AUD.
In the second step of the regression, a significant interaction emerged between early adolescent CD symptoms and depression in predicting both alcohol abuse and alcohol dependence. Post hoc probing of the interactions revealed a similar pattern of findings for alcohol abuse (see ) and alcohol dependence (see ). Depressive symptoms did not significantly differentiate non-AUD participants from those who developed alcohol abuse at low (relative risk ratio (RRR) = .717, 95% CI = .484 − 1.061, z = −1.664, p = .096) and moderate (RRR = 1.151, 95% CI = .846 − 1.565, z = .897, p = .370) levels of CD symptoms. However, increased depression was associated with a greater risk for developing alcohol abuse for individuals with high levels of CD symptoms (RRR = 1.842, 95% CI = 1.140 − 2.974, z = 2.496, p = .013). Similarly, depressive symptoms did not significantly differentiate non-AUD participants from those who developed alcohol dependence at low (RRR = .793, 95% CI = .541 − 1.164, z = −1.185, p = .236) and moderate (RRR = 1.163, 95% CI = .880 − 1.537, z = 1.061, p = .289) levels of CD symptoms. In contrast, higher levels of depressive symptoms were significantly associated with a greater risk for developing alcohol dependence for those participants with high levels of CD symptoms (RRR = 1.701, 95% CI = 1.174 − 2.465, z = 2.805, p = .005).
Interaction between conduct disorder symptoms and depression in predicting alcohol abuse by young adulthood. Predicted values are based on the log of the relative risk ratio.
Interaction between conduct disorder symptoms and depression in predicting alcohol dependence by young adulthood. Predicted values are based on the log of the relative risk ratio.
4.4 Post Hoc Analyses
Because no a priori hypotheses were made about interactions between early adolescent ADHD symptoms, depression, and anxiety in predicting AUD symptoms and diagnoses by young adulthood, two-way interactions between these facets of early adolescent psychopathology were not included in the primary analyses. However, exploratory analyses were conducted with the two-way interaction terms representing ADHD symptoms by depression, ADHD symptoms by anxiety/withdrawal, and depression by anxiety/withdrawal. These interaction terms were added to models predicting both AUD symptoms and diagnoses, after controlling for all potential confounds and the significant CD symptom by depression interaction. None of the parameter estimates for these interaction terms were statistically significant. These analyses are available upon request from the primary author.