As I mention in the post immediately below this one, I much liked Radley Balko’s TechCentralStation piece. I do think, though, that this line falls into a common error:
But I doubt that Easterbrook longs for the early 20th century, when 45% of American laborers toiled in the fields — and most of them could expect to live all of 47 years.
If life expectancy is 47 years, this does not mean that most American laborers could expect to live “all of 47” years. First, it means that the average lifespan of Americans born in 1900 was 47 years. If the 47 years were the median lifespan, then half of Americans could expect to live 47 or more years, or alternatively half of them could expect to die by age 47 (setting aside the tiny fraction that would live exactly 47 years, on the dot). This is already not quite the same as “most of [Americans] could expect to live all of 47 years.”
But the 47 years is the average, and since there are many more people dying on the far left end of the age distribution curve (near age 0) than on the far right (near age 94), the average is biased downwards from the median, and thus the median is likely to be considerably higher than the average. (Simple, because oversimplified, example: If in a group of 10 people, 3 die at age 1, 4 die at age 50, and 2 die at age 60, and 1 dies at age 90, the average lifespan is 41.3 years, even though the median is 50 — because more people die on the far left of the curve than on the far right, the average [41.3] is less than the median [50], and considerably more than half the people live to the average [41.3] age.) Thus, considerably more than half of all Americans born in 1900 would have lived to be over 47.
(Note also that the 47-year figure, like most life expectancy figures, asks how long people born in 1900 would have been expected to live on average. It doesn’t address what the quote literally refers to, which is how long people alive in 1900 would have been expected to live; I don’t know of any sources for such a number.)
Second, the life expectancy figures include the deaths of infants and children. Such deaths are tragic, of course, but infants and children aren’t literally “American laborers toil[ing] in the fields.” And even going beyond the literal, I think it paints a misleading picture to just cite a life expectancy of 47 picture when in reality we have very many children dying before age 10, but the survivors living on average until 60 or so.
In fact, according to this data, Americans who survived until age 10 in 1900 did have an average lifespan of about 60 years (the data is broken down by sex and race, so I don’t have the precise numbers, but 60 is likely the rough average). Not great for those who survived childhood, and awful for the children who died young and for those children’s parents — but not quite as grim as having most of American laborers being expected to live all of 47 years. (I have no evidence on the lifespan of American laborers who toiled in the fields, but I imagine that the data there was probably not that much different from the data for the country at large.)
In any case, this doesn’t materially undermine Balko’s piece, which I much like. But it is an important thing to remember whenever one hears life expectancy numbers.
UPDATE: D’oh! My original post had an error in the portion labeled “First,” because I foolishly characterized the life expectancy as a median rather than a mean. I’ve corrected that portion; thanks to reader Brock Sides for pointing this out to me.
FURTHER UPDATE: Mike Anderson (Mere Dicta) has some more on this.
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