car ownership and morality

Doug Skrecky (
Sat, 23 May 1998 17:14:50 -0700 (PDT)

Smith GD. Shipley MJ. Rose G.
Department of Epidemiology and Population Sciences, London School of Hygiene
and Tropical Medicine.
Magnitude and causes of socioeconomic differentials in
mortality: further evidence from the Whitehall Study.
Journal of Epidemiology & Community Health. 44(4):265-70, 1990 Dec.
STUDY OBJECTIVE--The aim was to explore the magnitude and causes of the
differences in mortality rates according to socioeconomic
position in a cohort of civil servants. DESIGN--This was a prospective
observational study of civil servants followed up for 10 years after baseline
data collection. SETTING--Civil service offices in London.
PARTICIPANTS--11,678 male civil servants were studied, aged 40-64 at baseline
screening between 1967 and 1969. Two indices of socioeconomic position were
available on these participants--employment grade (categorised into four
levels), and ownership of a car. MEASUREMENTS AND MAIN RESULTS--Main outcome
measures were all cause and cause specific mortality, with
cause of death taken from death certificates coded according to the eighth
revision of the ICD. Employment grade and car ownership were independently
related to total mortality and to mortality
from the major cause groups. Combining the indices further improved
definition of mortality risk and the age adjusted relative
rate between the highest grade car owners and the lowest grade non-owners of
4.3 is considerably larger than the social class differentials seen in the
British population. Factors potentially involved in the production of these
mortality differentials were examined. Smoking, plasma
cholesterol concentration, blood pressure, and glucose intolerance did not
appear to account for them. The pattern of differentials was the same in the
group who reported no ill health at baseline as it was in the whole sample,
which suggests that health selection associated with frank illness was not a
major determinant. The contribution of height, a marker for
environmental factors acting in early life, was also investigated. Whereas
adjustment for employment grade and car ownership attenuated the association
between short stature and mortality, height
differences within employment grade and car ownership groups explained little
of the differential mortality. CONCLUSION--The use of social
class as an index of socioeconomic position leads to underestimation of the
association between social factors and mortality, which may
be reflected in public health initiatives and priorities. Known risk factors
could not be shown to account for the differentials in
mortality, although the degree to which this can be explored
with single measurements is limited.