THE 1974 fuel crisis was a natural experiment. It presented the opportunity to test the hypothesis that a decrease in vehicular exhaust fumes would have a beneficial effect on health. During the first quarter of 1974 retail gasoline sales were reduced by 9.5% in San Francisco and Alameda Counties, California. Total exhaust emissions were reduced by an even greater amount because of hoarding of fuel and lowered highway speed limits. To assess the possible effects of this selective decrease in pollution, mortality rates from these two counties were examined. The rates for the first quarter of 1974 were compared with corresponding rates from the first quarters of 1970–73.
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