Multi-level Modelling of International Variations and Time Trends in Asthma and Allergic Diseases in Children and Adults

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This project will combine substantive research into asthma causes and time trends with developing statistical methodologies to handle complex multi-level datasets.The main data sources are from three linked studies:Phase I (1992-1995) of the International Study of Asthma and Allergies in Childhood (ISAAC) collected information by questionnaire on symptoms and risk factors for asthma, rhinoconjunctivitis and eczema from 721,602 children in 155 collaborating centres in 56 countries. Phase III (2001-2002) of ISAAC collected similar information from 1,187,496 children in 237 centres in 98 countries. The Global Asthma Network (GAN) will use the ISAAC methodology to collect similar data during 2016-2017 but with the extension of data on parents and extra questions on asthma management and the environment. To date, 88 centres from 34 countries have registered for GAN and registration is ongoing.The type of data collected for the studies includes information on symptoms and severity along with environmental and demographic data for three different age groups, one in childhood, one teenage and one adult. This fits in well with the MRC strategic research aims of investigating health through the life course, and understanding how lifestyles and environment affect health. Within each country at least one urban and one rural centre will be sought so the influence of the general environment on asthma can be explored. A sample size of at least 3,000 people per age group per centre will be used to give sufficient power to detect differences in the severity of asthma. In smaller island populations, all pupils in the age group and their parents will be selected.Starting with the existing ISAAC surveys, which have yet to be fully exploited with state-of-the-art statistical modelling techniques, and later combining it with the GAN survey data it will be possible to run integrated analysis on all three studies. This complex multi-level structure will contain multiple exposures on 3 age groups, at 4 different levels (person, school, centre and country) across up to 3 time points. For some centres there will be missing age groups and/or missing time points which will need to be addressed correctly to ensure the statistical inference is robust. This aligns well with the MRC skills priorities of quantitative and interdisciplinary skills by combining the development of novel statistical methodologies for large, multi-level datasets with their application on epidemiological questions of potential causes or risk factors for asthma and other allergic diseases.The results of this project should be useful to public health officials within multiple countries. Understanding the important risk factors at different levels improves the ability to positively impact the prevalence and severity of asthma and other allergic diseases through changing health policies. Outcomes will vary widely from country to country and this work will help estimate the impact of potential policy changes. In addition, the methodological developments will be useful for statisticians working in other areas of health research but with similarly constructed multi-level datasets.