Improving the self reporting of tobacco use: results of a factorial experiment

Objectives: To examine divergent estimates of smoking prevalence in two random digit dial surveys for the same population. Based upon internal and external reviews of survey procedures, differences in survey introductions ( general health versus tobacco specific introduction) and/or differences in the use of filter questions were identified as the most likely explanations. This prompted an experiment designed to investigate these potential sources of measurement error. Design: A randomised 2 x 2 factorial experiment. Setting: A random digit dial telephone survey from July to September 2000. Subjects: 3996 adult Californian respondents. Main outcome measures: A series of smoking prevalence questions in the context of a tobacco or general health survey. Results: Logistic regression analyses suggest that, among females, prior knowledge ( from the survey introduction) that a survey is concerned with tobacco use may decrease self reported smoking prevalence ( approximately 4% absolute prevalence difference). Differences in the use of filter questions resulted in almost no misclassification of respondents. Conclusions: The tobacco specific survey introduction is causing some smokers to deny their tobacco use. The data suggest that these smokers tend to be women that smoked occasionally. A desire by the participants to minimise their personal time costs or a growing social disapproval of tobacco use in the USA may be contributing to the creation of previously undetected survey artefacts in the measurement of tobacco related behaviours.