Agreement between two measures of alcohol consumption

Responses on the Quantity-Frequency Questionnaire (QF) were compared with those on the self-report diary. The QF was administered to 778 general practice patients prior to their consultation and the same patients completed the diary at home within 24 hours. The diary overestimated the number of nondrinkers in the population relative to the QF and classified a higher proportion of patients as heavy drinkers. The QF failed to detect 78% of heavy drinkers identified by the diary. Significantly (p < .001) more alcohol was reported to be consumed overall on the diary (mean, 10.51 drinks/week) than on the QF (mean, 6.87 drinks/week). The relationship between responses on the two measures was nonlinear. At low consumption levels patients indicated drinking twice as much on the diary as on the QF, but the magnitude of the reported consumption difference decreased with increasing consumption levels. The results are discussed in terms of their implications for self-report measures of alcohol consumption.