Mitchell’s Musings 10-9-2017: The Meaning of Life Daniel J.B. Mitchell From time to time, you see stories in the news media and other sources about “life expectancy.” There may be comparisons of the U.S. with other countries or with particular groups within the U.S. There may also be comparisons over time. Table 1 provides an example. === Table 1: Selected Life Expectancies at Birth in the U.S. (years) 2015
1900
-----------------------------------------------Both Sexes
78.8
47.3
Males
76.3
46.3
Females
81.2
48.3
-----------------------------------------------Males (2015)
Females (2015)
-----------------------------------------------Hispanic
79.3
84.3
White Non-Hispanic
76.3
81.1
Black
71.8
78.1
-----------------------------------------------Source: https://www.cdc.gov/nchs/data/hus/hus16.pdf#015. === You may see things on the table that you already know without seeing the numbers. For example, life expectancy has grown over time or females live longer than males. You may also see things that surprise you, i.e., that Hispanics have a longer life expectancy than non-Hispanic whites. But what precisely do these numbers mean? In essence, to calculate these figures, data on survival rates are used. What is the probability within the group that a newborn will reach age 1. What is the probability that a 1-year old will reach age 2, etc., based on current probabilities? So what is really being measured is what would happen - on average - to someone born today if these survival rates were indefinitely frozen.
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