How much alcohol do you buy? A comparison of self-reported alcohol purchases with actual sales.

BACKGROUND: Unrecorded alcohol has increased in the Nordic countries during recent years, above all in terms of cross-border trade. This implies that trends and levels of per capita consumption would look different without estimates of this source of alcohol, estimates that in Sweden and other countries are made through surveys. AIM: The overall aim is to analyse the validity of Swedish survey estimates of alcohol bought in the cross-border trade and possibly to develop weights that can be applied to such estimates. DATA AND
METHOD: The analysis consists of comparing self-reported purchases of spirits, wine, cider/alcopops and beer at retail monopoly (Systembolaget) during 2008 (n = 18,000) with actual sales during the same period overall and monthly.
FINDINGS: Of the recorded amount of purchases at Systembolaget, 87% was reported in the survey, compared with the 40-60% usually found for self-reported consumption. Significant differences across beverages were revealed, showing a lower coverage rate for beer and spirits and a higher coverage rate for wine and cider. Changes in purchases of all beverages were captured fairly well, at least changes taking place from one month to another.
CONCLUSIONS: Self-reported alcohol purchases achieve a higher coverage rate than found typically in studies based on self-reported use of alcohol. If adjustments are to be made to correct for underreporting in self-reported data on alcohol purchases, different weights should be applied to different beverages. Furthermore, at least major changes in how much alcohol is purchased in the population can be monitored using well-designed population surveys.