METHODS

 

The National Longitudinal Alcohol Epidemiologic Survey (NLAES) was a National probability survey sponsored by the National Institute on Alcohol Abuse and Alcoholism (NIAAA). In 1992, the U.S. Bureau of the Census administered for NIAAA face to face interviews with 42,862 respondents age 18 and older, mean age 44, residing in the non-institutionalized population of the contiguous states including the District of Columbia. 

Sample Design:

The multi-stage sampling approach used for NLAES was described by Massey et. al., 198916. Primary sampling units (PSUs) were stratified according to socioeconomic criteria and were selected with a probability proportional to their population size. Within PSUs, geographically defined secondary sampling units, referred to as segments, were selected systematically for the sample. The African American population was oversampled at this stage of the sample selection to secure adequate numbers for analytic purposes. Segments were then divided into clusters of 4-8 housing units, and all occupied housing units were included in the survey. Within each household, one randomly selected person age 18 and older was selected to participate. Young adults age 18-29 were oversampled at a ratio of 2.25:1.00 at this stage of sample selection to include a greater representation of this heavier drinking population subgroup. Weighting using the Survey Data Analysis Statistical Package (SUDAAN)17 adjusted for the deliberate oversampling of African Americans and persons age 18-29 and accounted for the complex sampling design of NLAES. The household response rate for this representative sample of the U.S. population was 91.9 percent and the sample person response rate was 97.4 percent. The overall response rate was 90 percent. 

Alcohol use and alcohol dependence assessment:

Measures of alcohol use and dependence were derived from the Alcohol Use Disorder and Associated Disabilities Interview Schedule (AUDADIS)18; a fully structured diagnostic psychiatric interview designed to be administered by trained interviewers who were not clinicians. 

The age of drinking onset was ascertained by asking respondents how old they were when they first started drinking, not counting small tastes or sips of alcohol. Drinking onset data was collected from respondents who were classified as current drinkers (persons who had consumed at least 12 drinks in the past 12 months) and former drinkers (persons who had consumed at least 12 drinks in any one year of their lives but not during the year prior to the interview). Only current and former drinkers were included in the analysis. In an independent test retest study before the full NLAES was conducted, the test retest reliability of the drinking onset variable was good with a Kappa of 0.7219.

The definition of lifetime alcohol dependence was based on the diagnostic criteria of the Diagnostic and Statistical Manual, Fourth Edition (DSM-IV). The AUDADIS interview included an extensive list of symptom questions that operationalize the DSM-IV criteria for alcohol dependence. Diagnosis of alcohol dependence required that in any one year a respondent meet at least three of the following seven criteria for dependence: 1) tolerance, 2) withdrawal or avoidance of withdrawal, 3) persistent desire or unsuccessful attempts to cut down or stop drinking, 4) spending much time drinking, obtaining alcohol, or recovering from its effects, 5) giving up or reducing occupational, social, or recreational activities in favor of drinking, 6) impaired control over drinking and 7) continuing to drink despite a physical or psychological problem caused or exacerbated by drinking. In the analysis, respondents were classified as either showing a alcohol dependence diagnosis in the past year, or at any time prior to the past year or never. The independent test retest study determined good reliabilities with Kappas of 0.76, and .0.73 for past year and prior to past year dependence diagnoses respectively19.

Family history of alcoholism was ascertained through a series of questions that asked about different types of first degree biologic relatives (i.e., parents, children and siblings). The respondent was asked how many of each type of relative lived to be at least 10 years old and how many were ever alcoholics or problem drinkers. An alcoholic or problem drinker was defined for the respondents in a manner consistent with DSM-IV criteria for alcohol use disorder

"By an alcoholic or problem drinker, I mean a person who has a physical or emotional problem because of drinking, problems with a spouse, family or friends because of drinking; problems at work because of drinking, problems with police because of drinking- like drunk driving-or a person who seems to spend a lot of time drinking or being hung over."

In a test retest study conducted in conjunction with the NLAES, the family history items showed good to excellent reliability with Kappas at 0.72 for fathers, 1.00 for mothers, 0.90 for brothers, 0.73 for sisters and 0.65 each for sons and daughters19. In this study a respondent was classified as Family History Positive (FHP) if any of their first-degree relatives were reported as having been an alcoholic or a problem drinker.

Current heavy drinking was determined by asking respondents, "During the past 12 months, about how often did you have five or more drinks of any type of alcohol in a single day?" Respondents were also asked, "About how often would you say you usually drank enough to feel drunk during the last 12 months? By drunk, I mean times when your speech was slurred, you felt unsteady on your feet or you had blurred vision."

We also constructed a measure of the frequency with which respondents drank five or more drinks during their period of heaviest drinking in their life. Respondents were asked whether there were periods in their life when they drank more than in the past year. Respondents who answered yes were then asked their frequency of drinking and the amounts they usually consumed on days they drank during this period. They were also asked what was the greatest amount they drank on any day during that period and how frequently they drank that amount. We used data from these questions as well as questions about frequency of drinking five or more drinks in the past year to determine their frequency of drinking five or more drinks during their lifetime period of heaviest drinking.

Taking risks that might lead to injury was assessed by a question, "In your life, did you ever get into a situation while drinking or after drinking that increased your chances of getting hurt - like swimming, using machinery, or walking in a dangerous area or around heavy traffic? Did that happen in the past 12 months?" Finally, life time and past year alcohol related injury involvement were explored by asking respondents "In your entire life, did you ever accidentally injure yourself under the influence of alcohol, for example have a bad fall, or cut yourself badly, get hurt in a traffic accident, or anything like that? Did this happen in the past 12 months?" 

Statistical Analysis:

All statistical analyses were conducted using the SUDAAN statistical package to account for the survey design 17. Age of drinking onset was categorized as under 14, each year separately from 14 through 20, and 21 or older and all analyses focused only on respondents who responded to this question. The significance of relations between age of drinking onset and respondent background characteristics was tested using chi square analysis. 

We examined the relation between age of drinking onset and frequency of heavy drinking, adjusting for background characteristics including history of alcohol dependence through a series of multiple logistic regression analyses. We examined the following outcomes as dichotomous variables, whether or not respondents:

  • drank at least 5 + drinks at least once per week in the past year;
  • drank to intoxication at least weekly in the past year;
  • drank 5+ drinks at least daily during the period when respondents drank most heavily.

Odds ratios and 95% confidence intervals were calculated describing the increased risk of these outcomes for those with drinking onset before age 14 and at each age from 14 through 20 relative to those who started drinking after age 21.

To assess whether age of drinking onset was related to injury outcomes, we also conducted multiple logistic regression analyses examining as dichotomous outcome variables, whether or not respondents ever or in the past year: 

  • got into a situation while or after drinking that increased their risk of injury
  • accidentally injured themselves under the influence of alcohol.

The regressions were conducted twice. First, we entered the personal social and demographic characteristics associated with age of drinking onset other than alcohol dependence and measures of heavy drinking frequency; then we added measures of alcohol dependence and heavy drinking. This was done to assess whether any relations between age of drinking onset and injury involvement were primarily a function of those who started drinking earlier in life being more likely to experience more frequent heavy drinking episodes.

We entered the frequency of heavy drinking during the respondent's heaviest drinking period into the regressions examining life time exposure to injury risks and injury involvement, and the past year frequency of heavy drinking measures into the regressions examining past year exposure to injury risk and injury involvement.

For consistency across models, the entire set of background variables was included in the analysis of each drinking and injury outcome.

 

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