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.

The hypothesis that late respondents are more similar to non-respondents than early respondents, could not be confirmed or rejected. Repeated mailings are effective in obtaining a greater sample size, but seem ineffective in improving the representativeness of alcohol consumption surveys.

Aim To compare data quality of two formats of the weekly recall measure (WR1 vs WR2) and the weekly quantity-frequency alcohol measure (QF1 vs QF2). Design Participants were randomly allocated to one of the four formats of alcohol measure. On aggregate level, formats were compared for mean number of alcohol units/drinking days and for item nonresponse. Respondents' problems with completing the questionnaire were assessed by cognitive interviewing. Findings No differences in alcohol consumption were found between WR1 and WR2, and item nonresponse was higher on WR2 than on WR1. QF2 yielded a higher mean number of drinking days/week than QF1 but no differences in number of units/week; QF2 had a higher item nonresponse rate than QF1. Most problems occurred in averaging and in reporting consumption according to the given instructions.Conclusions On an aggregate level, there were no differences in alcohol consumption between WR1 and WR2, but WR2 had a higher likelihood of item nonresponse. According to the 'more is better' principle, QF2 is preferred, but also has a higher item nonresponse than QF1. Interviewing uncovered problems and misreporting that could not be revealed by comparing aggregate scores.

Most general alcohol consumption population surveys are meant to represent the year consumption, although they actually ask only for habitual drinking and/or frequencies and quantities of binge drinking in the past months. These surveys typically cover about half of the alcohol sales figures. In order to enhance sales coverage and to reduce seasonal bias, we developed a year consumption questionnaire on the basis of daily and weekly drinking adding 13 categories of less-than-weekly drinking occasions over the year. As a first test we offered the new questionnaire together with a traditional typical week questionnaire, in different modes to various groups adding up to a purposive high diversity sample of 101 drinking persons (56 women, 44 men, 16-69 years old, mean age 34 years). After correction for overlaps between weekly habits and less-than-weekly occasions, the new questionnaire produces considerably higher reports of annual consumption, compared with the typical-week-based estimates of year consumption. Limitations of the study are discussed.