RESULTS


Sixty-five percent of respondents ever drank alcohol, 49 percent before age 21 and 3 percent before age 14. The mean drinking onset age was 19.0 years. Four percent were classified as alcohol dependent in the past year and 13 percent ever in their life.

Twenty-three percent of respondents reported driving a motor vehicle after having too much to drink ever in their life and five percent in the past year. Four percent of respondents reported ever having been in a motor vehicle crash because of their drinking, 0.2 percent in the past year. The earlier the age respondents began drinking, the greater the proportions who reported driving after drinking too much and motor vehicle crash involvement because of drinking ever in their lives and during the year prior to the survey. As can be seen in Figure 1, persons who began drinking before age 14 were 3 times more likely than those who began drinking after age 21 to report ever driving after drinking too much, 53 percent vs. 18 percent, and 4 times more likely to report doing so in the past year, 13 percent vs. 3 percent. As seen in Figure 2, respondents who began drinking before age fourteen were 7 times more likely than those who began drinking after age 21 to report ever being in a motor vehicle crash because of their drinking, 14 percent vs. 2 percent, and during the past year, 0.7 percent vs. 0.1 percent. The magnitude of differences tended to become smaller as the age of drinking onset became closer to 21. As seen in Figures 1 and 2, even after age 21, the older respondents were when they began to drink the less likely they were to drive after drinking or be in traffic crashes after drinking.

Several subgroups in the study were significantly more likely to have begun drinking at younger ages: male respondents, younger respondents, those with less than a high school education, persons never married, and persons who currently or ever smoked or used illicit drugs and respondents with a current (past year) or lifetime diagnoses of alcohol dependence (all relations p<.001; data available upon request).

To control for these potentially confounding characteristics, we entered those background characteristics into a series of multiple logistic regression analyses examining the following outcomes as dichotomous variables: whether or not respondents drove after drinking too much, or were in a motor vehicle crash because of their drinking. Each of these outcomes was examined ever during the respondent's life and during the year prior to the interview.

Respondents who began drinking at an earlier age were significantly more likely to report that they drove after drinking too much ever and in the past year. Further, they were significantly more likely to have ever been involved in a motor vehicle crash after drinking too much. For each study outcome, the odds ratio and 95% confidence intervals for respondents who began drinking each year from less than age 14 through 20 relative to those who began at age 21 or older was examined separately. Persons starting at age 21 and older were analyzed as a group for comparison because the minimum legal drinking age is 21. Results are summarized in Figures 3 and 4.

The strongest relationships were observed when comparing respondents who started drinking at age 14 relative to those starting at age 21 and older. Persons who began drinking when they were age 14 were 3.4 (95% CI 2.7, 4.3) times more likely than those who began after age 21 to report ever driving after drinking too much and 2.33 (1.7, 3.2) times more likely to do so in the year prior to the survey. Further, they were 4.1 times more likely to report being in a motor vehicle crash after drinking too much ever (95% CI 2.9, 5.8) and in the past year (95% CI 1.5, 10.9). As can be seen in the figures, these relationships tended to be stronger for those whose age of drinking onset was younger. Also the relations were stronger when we examined whether respondents ever in their life drove after drinking too much or were ever in a motor vehicle crash because of drinking as compared with those who experienced these outcomes in the past year. Respondents who began drinking in each age group under 21 relative to those starting after age 21 were significantly more likely to report ever driving after drinking too much and ever being in a motor vehicle crash because of their drinking.

We also repeated the logistic regression analysis examining only the subgroup of respondents who drank but never experienced alcohol dependence (n=21,462). Just over half the sample and 79% of persons who ever drank this group represented 35% of those who reported motor vehicle crashes after too much drinking ever during their life and 28% of those reporting such crashes in the year prior to the interview. Those who started drinking in each age group under 21 were significantly more likely than those who started drinking after age 21 to have ever and in the past year been in a motor vehicle crash after drinking too much. (Figure 5).

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