FIGURE 4-1 Mean daily deaths in London versus mean smoke (µg/m3), 1958–1972. Source: Schwartz and Marcus, 1990, with permission.

lates and the daily rate of mortality for each year in London, the regression coefficients of particulates were consistent as well.

Acute mortality from exposure to hazardous industrial products occurred in Bhopal, India, in 1984. The analytical issues raised in studies of such acute events are relevant to the study of hazardous wastes. Longitudinal studies of such episodes within a single population are confounded by multiple factors that occur when different geographic regions are compared. These issues are discussed in more detail in the section on longitudinal studies of morbidity.

CROSS-SECTIONAL STUDIES OF MORTALITY

Cross-sectional studies provide epidemiologic snapshots or pulses of a given area at one point in time. Recent computer technology has permitted easier preparation of maps of comparative mortality data from different regions of the U.S. and Canada. Of more relevance to



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