The extraordinary increase in life-expectancy that occurred early in t
his century has been attributed largely to non-medical factors. Life-e
xpectancy has continued to rise, and medical care can; now be shown to
make substantial contributions. Three of the seven years' increase in
life expectancy since 1950 can be attributed to medical care. Medical
care is also estimated to provide, on average, five years of partial
or complete relief from the poor quality of life associated with chron
ic disease. The association of social factors with health is well-know
n, but except for occupation, it is not known how they might act or wh
ether they are proxies for some other yet to be identified factor.