Abstract
BACKGROUND: Prior studies adjusting self-reported measures of alcohol intake for drink size and ethanol (EtOH) content have relied on single-point assessments. METHODS: A prospective 28-day diary study investigated magnitudes of drink-EtOH adjustments and factors associated with these adjustments. Transdermal alcohol sensor (TAS) readings and prediction of alcohol-related problems by number of drinks versus EtOH-adjusted intake were used to validate drink-EtOH adjustments. Self-completed event diaries listed up to 4 beverage types and 4 drinking events/d. Eligible volunteers had ≥ weekly drinking and ≥3+ drinks per occasion with ≥26 reported days and pre- and postsummary measures (n = 220). Event reports included drink types, sizes, brands or spirits contents, venues, drinks consumed, and drinking duration. RESULTS: Wine drinks averaged 1.19, beer 1.09, and spirits 1.54 U.S. standard drinks (14 g EtOH). Mean-adjusted alcohol intake was 22% larger using drink size and strength (brand/EtOH concentration) data. Adjusted drink levels were larger than "raw" drinks in all quantity ranges. Individual-level drink-EtOH adjustment ratios (EtOH adjusted/unadjusted amounts) averaged across all days drinking ranged from 0.73 to 3.33 (mean 1.22). Adjustment ratio was only marginally (and not significantly) positively related to usual quantity, frequency, and heavy drinking (all ps < 0.10), independent of gender, age, employment, and education, but those with lower incomes (both p < 0.01) drank stronger/bigger drinks. Controlling for raw number of drinks and other covariates, degree of adjustment independently predicted alcohol dependence symptoms (p < 0.01) and number of consequences (p < 0.05). In 30 respondents with sufficiently high-quality TAS readings, higher correlations (p = 0.04) were found between the adjusted versus the raw drinks/event and TAS areas under the curve. CONCLUSIONS: Absent drink size and strength data, intake assessments are downward biased by at least 20%. Between-subject variation in typical drink content and pour sizes should be addressed in treatment and epidemiological research.