Example 1.10 The line graph shown in Figure 1.6 displays the trend in rates
of malaria reported in the United States between 1940 and 1989 (proportion
100,000 as above).
1.2 RATES
The termrateis somewhat confusing; sometimes it is used interchangeably with
the termproportionas defined in Section 1.1; sometimes it refers to a quantity
of a very di¤erent nature. In Section 1.2.1, on thechange rate, we cover this
special use, and in the next two Sections, 1.2.2 and 1.2.3, we focus onratesused
interchangeably withproportionsas measures of morbidity and mortality. Even
when they refer to the same things—measures of morbidity and mortality—
there is some degree of di¤erence between these two terms. In contrast to the
static nature of proportions, rates are aimed at measuring the occurrences of
events during or after a certain time period.
1.2.1 Changes
Familiar examples of rates include their use to describe changes after a certain
period of time. Thechange rateis defined by
TABLE 1.5
Crude Death Rate
Year per 100,000
1984 792.7
1985 806.6
1986 809.3
1987 813.1Figure 1.5 Death rates for U.S. women, 1984–1987.RATES 11