Assessment of alcohol consumption by mailed questionnaire in epidemiological studies:: Evaluation of misclassification using a dietary history interview and biochemical markers

Background: Self-reported information on alcohol from questionnaires is generally assumed to introduce misclassification of consumption, mainly in the direction of underestimation. The aim of this study was to evaluate self-reported information on alcohol consumption from a mailed questionnaire by comparing to a dietary history interview and biochemical markers of alcohol intake. Subjects and Methods: For 76 male twin pairs of the Finnish Twin Cohort Study aged 40-70 years information on self-reported alcohol consumption was collected through mailed questionnaire and dietary history interview. Carbohydrate-deficient transferrin (CDT), Gammaglutamyltransferase (Gamma-GT) and mean corpuscular volume (MCV) were determined from blood samples. Results: Mean levels of CDT, gamma-GT and MCV showed a rise with increased self-reported alcohol consumption already at low levels of reported consumption (<20 g alcohol/day). There was a positive correlation between reported amount alcohol intake per day and levels of CDT (r = 0.46), gamma-GT (r = 0.32) and MCV (r = 0.36) but within the high consumption group (>= 30 g/day) there was no such correlation. The questionnaire had sensitivity of 28-43% and specificity of 89% for identification of high consumers of alcohol using the biochemical markers as reference and sensitivity 41% and specificity 94% using the dietary history interview as reference. Sensitivity was improved when information on binge drinking (82%) or possible drinking problems (73%) was considered. Conclusion: Comparison to dietary history interview as well as to biochemical markers indicate that self-reported information on alcohol consumption from a mailed questionnaire may be used to distinguish between groups with different levels of alcohol consumption. The suggested misclassification of high consumers implies that only strong associations between high alcohol intake and disease are likely to be detected in studies based on questionnaire data.