BELCOHORT: towards a population-based cohort for health research and policy support in Belgium

Abstract Background In the past decades much progress has been made in Belgium in the development and valorisation of population-based data collections which are directly or indirectly related to health. New surveys have been set up and the use of medico-administrative and environmental data for public health research gained momentum. However, no infrastructure is currently in place to link survey data with existing sources in a longitudinal perspective to address research questions directly relevant to health policy. BELCOHORT is a three-year pilot project aimed at developing a population based cohort enriched with these different data sources. The project is considered as a step towards a large population cohort in Belgium. Methods A first wave of participant recruitment was organized in February 2024 using the Belgian national register as a sampling frame, and 41,153 households were invited (targeted sample of 5000 individuals aged 18-69). A first baseline survey (online and paper) was organized and an annual follow-up is planned. Linkages procedures will be implemented with administrative data and geospatial data on air pollution and green space. The inclusion of data from physical examinations and biological samples will be explored. Results In the first recruitment wave the individual response rate was only 2.5%, leading to a sample of 1,947 participants. The sample showed an under-representation of women (45%), people aged 18-24 years (2%) and low educated people (21%). In total, 23% of participants opted to complete the first baseline questionnaire on paper. Stakeholder meetings have been started to implement the individual and geospatial linkages. Conclusions This project generate insights that will assist in methodological choices in the development of a large population cohort in Belgium. In the second recruitment lessons learned from the first data collection will be used to improve the response rate as well as the participation of under-represented groups. Key messages • This study provides insights on how existing population-based data collections including administrative and environmental data can be valorized in setting up a population cohort. • Recruitment strategies for a population cohort should be tested thoroughly and adapted in order to obtain a well-balanced sample composition.