Non-response bias in a sample survey on alcohol consumption

In a non-response follow-up study, non-respondents of the original mailed questionnaire were approached again by house visits in order to compare their alcohol consumption with that of the respondents of the same mailed questionnaire. Differences in alcohol consumption between respondents and non-respondents were found. There is strong evidence for overrepresentation of non-response among abstainers, but weak evidence among frequent excessive drinkers.