Declining Death Rates
The 2007 Statistical Abstract of the United States lists death rates per 100,000 population.
The 1951 Statistical Abstract of the United States lists death rates per 1000 population.
In 1949, the death rate of 1-4 year olds per 1000 population was 1.5 (itself a huge improvement over 1900’s 20). In 2003, the death rate of 1-4 year olds per 100,000 population was 32.
If the denominator hadn’t been changed, modern tables would be hard to read because the numbers would not be whole numbers.