| Only a limited percentage
of a population satisfies all criteria of ‘pulmonary
leaving only a small reference group. The populations of Vlaardingen
and Vlagtwedde (the Netherlands), who took part in a longitudinal
epidemiological study of lung health carried out by the TNO
Working group Epidemiology of CNSLD in the 1960-1980s may serve as an example.
Among adult men investigated by staff of the Physiology Department
of Leiden University fewer than 13% of men and than 48% of
women were lifelong non-smokers.
|Among women, 70% had never experienced chronic
respiratory symptoms, in men the corresponding percentage was 65%.
|Applying both criteria, about 1 in 10 males
were assigned to the reference group on the basis of respiratory
symptoms and smoking habits; in women only one third fulfilled
the combined set of criteria.