| Summary: | The Obstructive Lung Disease in Northern Sweden study's (OLIN) overall aim is prevention of obstructive airways diseases; asthma, chronic bronchitis and chronic obstructive pulmonary disease (COPD). The first part of the OLIN study was a cross- sectional study in three phases, which aimed to estimate the prevalence obstructive lung diseases and to collect data on possible determinants of diseases. This thesis is based on the first part of the OLIN study, and on a postal survey mainly performed in order to evaluate the external validity of the first part of the project Aims: * To assess the prevalences of asthma, chronic bronchitis and respiratory symptoms in adults. * To compare the influence of various diagnostic criteria on prevalence. * To identify subjects with obstructive lung diseases, in particular asthma, for case-referent and prospective longitudinal studies. * To examine whether the trend towards an increase in the prevalence of asthma persists. * Study factors that may influence the development of obstructive lung diseases; age, gender, smoking habit, occupation, socio-economic group, population density and area of domicile. The first part of the OLIN study consisted of three phases. A postal questionnaire regarding respiratory symptoms and diseases, smoking habit and profession was sent to all subjects aged 35-36 y, 50-51 y and 65-66 y (n=6,610) living in eight representative areas of Sweden's northernmost province; 86% completed the questionnaire. Those reporting symptoms suspicious of asthma or chronic bronchitis (n=l,340), together with a stratified sample (n=315) of those not suspected of having the diseases according to the postal questionnaire, were invited to structured interviews and lung function tests. The prevalence of asthma, 5- 6% according to both the postal questionnaire and to the structured interview, prompted a validity study, which included bronchial provocation tests. While the prevalence remained unchanged, the validity study better identified the subjects with asthma and chronic ...
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