Intra-Individual Variability in Self-Reported Use of Non-Steroidal Anti-Inflammatory and Analgesic Medicines Depending on Mode of Data Collection - Observations from the Population Study of Women in Gothenburg, Sweden.

Background Self-report by questionnaire is one of the main methods to collect data on drug utilization. There are several modes of data collection by questionnaire, differing in the way of delivering the questionnaire to respondents and in the administration of the questions, both influencing the recall and participation rates. The aim of this study was to compare different modes of data collection for self-reported use of non-steroidal anti-inflammatory (NSAIDs) and analgesic medicines. Methods Data on 573 women (38 or 50 years) were retrieved from the Population Study of Women in Gothenburg. Data on medicine use were collected using two different modes: (1) a self-administered questionnaire with closed-ended medicine-specific questions; and (2) an interviewer-administered questionnaire with open-ended questions. Cohen's kappa statistics were applied to assess the agreement of the two modes. Results The proportion of participants that reported use of NSAIDs and analgesics was higher with the self-administered questionnaire compared with the interviewer-administered questionnaire (69.3% vs 58.5%, p <0.001). The overall agreement between the two modes of data collection was fair (Ⱪ=0.27), ranging from none for antimigraine preparations to fair (Ⱪ=0.36) for NSAIDs. A higher proportion of the participants aged 38 years reported use of NSAIDs and analgesics compared with the 50-year olds. In the regression model using data from the self-administered questionnaire, all four categories of bodily pain were significant predictors for use of NSAIDs and analgesics. The most severe reported bodily pain was the only significant predictor in the model using data from the interviewer-administered questionnaire. Conclusion This study showed that use of a self-administered questionnaire with closed-ended medicine-specific questions identified more users of NSAIDs and analgesic medicines compared with an interviewer-administered questionnaire with open-ended questions. Reported use according to the self-administered questionnaire was also more strongly associated with experienced pain.