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Invited commentary: never, or hardly ever? It could make a difference.

A paper showing that about one half of persons stating lifelong alcohol abstinence had previously reported drinking (Am J Epidemiol 2008;168(8):866-871) reopens debate about the validity of this frequently used referent group in alcohol-health studies. Misclassification of lifelong abstainers could result in underestimation of harmful effects of heavy drinking and overestimation of benefits of lighter drinking. Imprecise and unreliable ascertainment of alcohol intake is the rule in the area of alcohol epidemiology research. However, inaccurate ascertainment of past infrequent drinking may have less effect upon outcome estimates than the consequences of other measurement errors such as underreporting of intake. Communication about alcohol-health relations would be improved if all research reports explicitly described queries and methods by which alcohol intake was categorized and if limitations were always frankly acknowledged.