Strengths and limitations
This study used state-of-the-art methodology to address important questions relating to alcohol misuse at age 17–18. An important strength of the study is that it included a good measure of alcohol misuse. This was not simply a quantity-frequency measure of alcohol consumption. Rather, a latent variable was used that was made up of frequency of heavy drinking, drunk driving and other problems relating to alcohol use. The missing data analyses used in this study allowed a much stronger model test than could have been conducted without these procedures. The longitudinal nature of the data strengthens the plausibility of causal interpretations, although, clearly, these results require replication.
Two limitations of this study should be acknowledged. First, the prospective measure of age of initiation suffered from left censoring in that some students had already initiated use at the start of the study. The retrospective measures should have compensated for this problem, in that they did not suffer from left censoring, but the compensation may not have been complete. In order to take this left censoring into account, we estimated the model with the grade of initiation variable set to missing if the participant initiated alcohol use at grade 6 (age 11–12) or earlier. Using this approach, the interpretation of regression weights involving age of initiation, especially the path from beliefs about alcohol harm (age 11–12) to age of initiation, was more clear cut. All regression weights that were significant in the original model were also significant in this test, with the exception of school bonding predicting age of initiation.
Second, all measures of age of initiation suffered from right censoring since 26% of the sample reported no use of alcohol by age 17–18. However, the retrospective reports were considered to be missing if the students had not yet begun to use by age 17–18, thus the missing data procedure used in this study gave these people less weight in the analyses. This helped to mitigate the problem of right censoring.
The present study investigated two questions concerning the role of age of initiation in the development of alcohol misuse. These questions were examined using data from an ethnically diverse sample of students followed for 7.5 years beginning in the fifth grade at age 10–11.
The first question concerned whether age of initiation mediated the effects of family, school, peer and individual risk factors for alcohol misuse among adolescents. The results showed that the younger individuals are when they begin drinking alcohol, the greater their level of problems associated with alcohol misuse. Further, the results showed that age of initiation of alcohol use was an important mediator of the effects of ethnicity, parents' drinking, proactive parenting, school bonding, friends' alcohol initiation and perceived harmfulness of alcohol on alcohol misuse at age 17–18. That is, parents' drinking, proactive parenting, peer influences and perceptions of the harm of drinking, all measured in late childhood, affect the age of alcohol initiation, which, in turn, affects alcohol misuse in late adolescence. In fact, with the exception of gender, there was not a single significant effect on age 17–18 alcohol misuse that was not mediated by age of initiation.
The results confirm that peers' alcohol use is a strong predictor of adolescent use and misuse of alcohol. Again, the effect of peers' alcohol use in late childhood on alcohol misuse at age 17–18 is mediated through the age of initiation of alcohol use. Children with alcohol-using peers at age 10–11 are more likely to initiate alcohol use early and to misuse alcohol later in adolescence.
The results also suggest that parental behavior plays a central role in adolescent use and misuse of alcohol. Parental drinking affected adolescent alcohol misuse in several ways. The children of drinking parents were less likely to see drinking as harmful and more likely to start drinking earlier. Both these attitudes and behaviors, in turn, predicted greater alcohol misuse at age 17–18. Parental drinking may also be mediated by friends' alcohol use in predicting alcohol misuse in adolescence. Children of drinking parents may feel less inhibited from forming friendships with other children who have tried alcohol at age 10–11, reflecting a selection effect (Hansen et al., 1987
Positive parenting methods also appear to inhibit adolescent alcohol misuse. Children of parents who communicated and were involved with their children at age 10–11, who set clear expectations for children's behavior, who practiced good supervision and consistent discipline, and who minimized conflict in the family, were more likely to see alcohol use as harmful at age 11–12, less likely to initiate alcohol use early, and, in turn, were less likely to misuse alcohol at age 17–18.
The effect of ethnicity on later alcohol misuse was also found to be mediated by age of initiation. White children generally began using alcohol earlier than did children of other ethnic backgrounds, and were, in turn, more at risk for later alcohol misuse. This effect may also be mediated by parental drinking. The fact that white parents drank more than nonwhite parents could also have mediated the effect of ethnicity on later alcohol misuse.
The second question concerned whether the mediation model would help us understand known gender differences in the severity of alcohol misuse. The strongest result in the present study was a significant direct relationship between gender and age 17–18 alcohol misuse (males misused more than females). That is, over and above the mediated effects already described, which apply to both males and females, there was a significant residual effect of gender on alcohol misuse that was not explained by variation in the age of initiation between males and females. However, another gender effect that was potentially mediated by age of initiation was the effect on proactive parenting. Parents in the present sample were more likely to employ proactive parenting with their female children.
Further research is needed to identify the source of the significant direct effect of gender on alcohol misuse at age 17–18 observed here. The fact that no main effect of gender on age of initiation was found indicates that the differences in levels of alcohol misuse between males and females at age 17–18 result from factors arising after alcohol use has been initiated. Norms regarding the acceptability of alcohol misuse in mid to late adolescence may differ for males and females.
Implications for prevention
These results have important implications for prevention programs seeking to reduce alcohol misuse. First, they indicate that efforts to delay the initiation of alcohol use as a prevention strategy are well conceived. The importance of age initiation found here indicates that delaying the age of initiation should be a goal of programs seeking to prevent alcohol misuse. Although further work is needed to identify how males and females reach different levels of alcohol-related problems, the strong association between age of initiation and later alcohol problems indicates that delaying the age of onset of alcohol use should reduce alcohol misuse for both males and females.
Further, the results suggest the promise of prevention programs that strengthen proactive parenting. These data suggest that programs should teach parents to set clear expectations for their children's behavior; to monitor and reinforce their children's behavior consistently and appropriately; to educate their children about the potential risks of alcohol use, even if the parents drink; to encourage their children to delay alcohol initiation; to help their children avoid or resist the influence of alcohol-using peers; to communicate and be involved with their children; and to manage family conflict effectively. These proactive parenting practices help delay alcohol initiation and, thereby, help prevent later alcohol misuse.
Interventions seeking to prevent alcohol misuse also should target elementary and middle school children directly. These results indicate that increasing the perceived harmfulness of alcohol use among children at ages 11–12 should delay the initiation of alcohol use, which, in turn, should reduce alcohol misuse at age 17–18.