Friday, March 13, 2009

Medieval Life Expectancy

Shanna Worthen (aka "Owlfish") has a discussion going on about medieval life expectancy, and she's hit on one of my pet peeves: the misleading way we talk about life expectancy.

My whole life, I've heard life expectancy numbers batted around for the Middle Ages -- and they have always been suspiciously round, usually around 30. As Worthen and her commenters point out, in order to arrive at that sort of figure, you have to do some statistically naive things, and talk about "life expectancy" in a misleading way.

It reminds me of the slick way people use statistics politically. For example, whenever a politician cites a figure that "such-and-such millions of Americans are without private health insurance," he's trying to pull a fast one, because that figure often includes those who are already covered under Medicare and Medicaid. A reasonable person, however, hearing that statistic in a stump speech, is going to assume that those millions of people are without any kind of health care. In fact, usually, the goal of someone using such a figure is to raise the number of people on government health care, thereby ensuring that next year they can say "such-and-such millions more Americans are without private health insurance" -- because those people have left the private market having been picked up by the same government entitlement the pol is pushing. Arguably, what the politician is saying is true, but a reasonable person without the benefit of time to parse the phrase will be misled.

Similarly, the 25 year life expectancy figure is misleading. It suggests that 30 is old, and 50 is absolutely ancient. That's not true, though. People in the Middle Ages lived just as long as people do today -- it's the average that's different. Walk into any village of reasonable size, and you'd find some old gaffer or widow of 80+ years. What you wouldn't find is a Miami retirement community filled with such people.

Why did I use health care as the example of misleading statistics? Because every so often we read in the paper that there's some sort of medical advancement that's going to "raise life expectancy," and the reporter seems to think that means humans will live longer.

We won't. While the average might go up, our bodies still have an expiration date. More and more of us might push 100, but we're not about to start living to 200+. Consider this: If we accept as a given that the average life expectancy of the Middle Ages was 25, then life expectancy has tripled, right? Since we know from both historical and archaeological records that some people lived to 80+ years in the Middle Ages, wouldn't that mean that people are living three times as long? Shouldn't there be some 240 year olds running around, grousing that things just aren't the same since Thomas Jefferson died?

And therein lies the problem. Even if the statistic is accurate, people hear something very different than the statistic is saying. A stat talking about life expectance tripling is about the average tripling, but the way it is popularly perceived is that the length of time people live has tripled. And, of course, it isn't. If you're old enough to read this, a century from now you'll be dead, no matter how much life expectancy rises.


  1. I guess if you made it through the various childhood diseases, and then avoided the biggies like smallpox or plague, you might have lived just as long back then as we do today. I'm proofreading a book right now on smallpox, and that was a doozy -- but then if you survived, you were immune for life.

    What I don't know enough about is medieval nutrition. I always hear about how the lower classes were actually better off than the upper class -- more fiber, less possibly toxic stuff like roasted peacocks restuffed into their skins, etc. But I wonder if that's really so.

  2. I've been dealing with this issue since my first year of teaching when a unit in our Western Civ reader that set a life-expectancy for early modern Europe at 42 made several students insist that you were aged and decrepit before forty, then!

    We broke it down in some detail to show how the high rate of infant mortality and the problems of disease, war, injury and childbirth were all factors that increased your chance of an early death. Now I teach an entire seminar on the early modern life cycle where we can explore the question in more detail but I still have to spend time exploding the myth of what life expectancy means in the minds of my students.

  3. I beg to differ -- a century from now, my brain will have long been transferred into another shell.

    My original body will have of course perished, so I guess you're kinda right... :P

  4. It's the persistent problem of historians and indeed journalists who didn't do enough maths to understand the difference between a mean and a median. The mean age of death in the Middle Ages was a lot lower than now because of the number of infant deaths and deaths by disease and childbirth, but the median was as you observe probably roughly similar. And this was the sort of maths I was doing age 15, but people don't seem to remember what `average' actually means when they get fed it off a news report or `scientific study'.

  5. I'm looking for data on medieval adult mortality. Any idea where I may look?

    I hear that once you survived the age of 15, warfare if you were a male and childbirth if you were a female then you would live about as long as we do now. I wonder how accurate that is? Surely disease must have taken a higher toll, especially given the absense of health care in a modern sense and especially antibiotics.

    BTW when they say that someone back then died of 'plague', was it always bubonic plague or did 'plague' simply mean 'epidemic disease?

  6. BTW I looked at the birth and death dates of the medieval dukes of the house of Burgundy as given on the Wikipedia page Duke_of_burgundy and where possibly calculated the age of their father at their birth. It turns out that most were born when their father was between 24 and 36 y-o and most lived into their fifties, though about a third died in their thirties and forties. Only one lived to be 65. This is only twelve men from high society, but interesting anyway.