Only few data have been published about non-responders in epidemiological s
tudies on respiratory diseases. The aim of this study was to examine the ch
aracteristics of the non-responders and the reasons for non-response in a s
urvey of respiratory health. All 9132 subjects, born 1925-1926, 1940-1941,
1955-1956 and 1970-1971 and living in eight representative areas in Norrbot
ten, Sweden, were invited to a prevalence study on asthma, chronic bronchit
is and respiratory symptoms. The response rate was 85%. A sample of the non
-responders from the cross-sectional postal questionnaire study was contact
ed by telephone and interviewed using the same questionnaire as had been us
ed in the postal survey. Of the 1397 non-responders a stratified sample of
182 subjects were selected for this study and 144 agreed to participate. Th
e response rate was increasing by increasing age. The main reason for non-r
esponse was that the subjects had forgotten to mail the questionnaire, lack
of interest or lack of time. There were significantly higher proportions o
f current smokers and manual workers among the non-responders. The prevalen
ce rates of wheezing, longstanding cough, sputum production, attacks of bre
athlessness, asthma and use of asthma medicines were significantly higher a
mong the non-responders compared with the responders according both univari
ate and multivariate logistic regression analyses, in which the influences
of age, sex, smoking habits, socioeconomic group and area of domicile were
taken into account. The prevalence of respiratory symptoms and diseases was
slightly underestimated in the postal survey.