Social class, level of education, and occupation
are closely correlated, and some of the
social gradient in respiratory diseases may be
caused by occupational exposure. The extent
of confounding by occupation in epidemiological
studies will depend strongly on the spectre
of occupational exposure in the population
under study. However, several findings indicate
that confounding by occupational exposure
does not fully explain the association. Women
generally do not hold jobs with major exposure
to dusts and fumes that potentially cause respiratory
disease, yet socioeconomic differences in
lung function are found in both sexes,
although most studies indicate that they are
smaller in women.