Changing Sex Differentials in Leukemia

Abstract

Average, iannual, age-specific mortality rates of leukemia for each sex and race in the United States were computed directly from published vital and census statistics (4-7) for eight 5-year periods and four 10-year periods from 1921 to 1960. These rates were used to calculate s,ex mortality ratios (SR==male-to-female death rates) for the various age groups in the white and nonwhite populations. A linear regression analysis determined whether the SR changed in relation to time; calculations were made of (a) slopes of lines generated by plotting each of the SR against calendar periods, thus showing the direction and magnitude of each trend, and (b) tests for independence, which provided a measure of the statistical significance and consistency oif the trends. The SR among whites, along with the agesex-specific mortality rates of leukemia, are shown in table 1 for the eight 5-year periods. Two changes over time in SR are nolteworthy: (a) a significant decrease for each of the childhood age groups (less than 1, 1-4, and 5-14 years); and (b) an increase for each a.ge group over 24 years, which is significant between 35 and 74 years. These coincidental, contrasting trends are illustrated by plotting the average annual SR for the four 10-year calendar periods (fig. 1). Demonstrated also is a consistent bimodal curve for the SR: the first peak occurred with the group 5-14 years of age in 1921-40 and shifted to the 15-24 year group in 1941-60; a second peak has become increasingly evident over time with the age groups above 64 years. When the SIR were arranged according to 10-year birth cohorts, there were no deviations from the patterns observed in figure 1. Among nonwhites (table 2), the SR ha,ve not shown consistent or significant trends, with the exception of a decline in the group less than 1 year of age. Irregularities in the nonwhite rates. and ratios may be attributed to the relatively small number of deaths from leukemia in that population.