Design and respondent selection of a population-based study on associations between breast cancer screening, lifestyle and quality of life

BACKGROUND: Only few studies have integrated breast cancer screening, lifestyle, and quality of life. Potential bias due to selective non-response may disrupt associations being investigated. We describe the design of a Finnish population-based study on associations between breast cancer screening and various indicators for lifestyle and quality of life, and evaluate the level of bias among the respondents from the first study rounds over 2 years. METHODS: The study target population of 10 000, 49-year-old women was randomly drawn from the Finnish National Population Registry. The data included birth year, marital status, municipality, and primary language. Data on education were retrieved from Statistics Finland. Questionnaires focusing on lifestyle-related risk factors and quality of life were sent to the target population in 2012–13, 1 year before the first invitation to organized breast cancer screening. We evaluated associations between willingness to respond and demographic characteristics in the eligible study population. Additionally, we examined associations between the demographic characteristics and the Satisfaction With Life Scale (SWLS), and evaluated the impact of non-response using inverse probability weighting and multiple imputation. RESULTS: The questionnaire response proportion was 52.4 %. Compared to non-respondents, respondents were more often married, academically educated, and native speakers of Finnish or Swedish. Nevertheless, the estimates of the SWLS among the respondents were in line with those corrected by non-response in the eligible study population. CONCLUSIONS: Based on the SWLS, the respondents are representative of women in the entire eligible study population.