I've long thought that life expectancy statistics were odd. Encyclopedias treat nation's life expectancies as numbers on par with square mileage. But in reality, doesn't this require a bunch of assumptions about future health developments?
At least according to Wikipedia, demographers "solve" this problem by completely ignoring it. So-called "life expectancy at birth" numbers are mechanically calculated based on current deaths:
Life expectancy is by definition an arithmetic mean. It can be calculated also by integrating the survival curve from ages 0 to infinite (the ultimate age, sometimes called 'omega'). For an extinct cohort (all people born in year 1850, for example), of course, it can simply be calculated by averaging the ages at death.
Note that no allowance has been made in this calculation for expected changes in life expectancy in the future. Usually when life expectancy figures are quoted, they have been calculated like this with no allowance for expected future changes. This means that quoted life expectancy figures are not generally appropriate for calculating how long any given individual of a particular age is expected to live, as they effectively assume that current death rates will be "frozen" and not change in the future. Instead, life expectancy figures can be thought of as a useful statistic to summarise the current health status of a population. (emphasis added)
Bottom line: Unless you think that health won't improve in the future, official statistics are selling your longevity short. Plan accordingly!
There are life tables that do take changing trends in life expectancy into account (I've built a generic tool to estimate an individual's basic life expectancy based upon 2002 data.) The problem of course is that even these don't drill down to cover an individual's particular health history (Do they smoke? Is there a family history of heart disease? Etc.) For factors like these, other tools have been developed for the purpose of better determining one's life expectancy.
On top of that remember that if you're middle aged now then chances are you'll live longer than average life expectancy anyway.
If life expectancy is 76 then a fit and healthy 74 year old shouldn't be expecting to die in two years time - since they've been alive people younger will have died and therefore anyone approaching the average is more likely to finish up "higher than average"
So there's two reasons to be confident about life expectancy: firstly the simple arithmetic, and secondly the measurement issues you've raised.
Hmmm. I feel Cowens "It's later than you think" will bring more fruit.
Why do you assume the trend is upward and stable? It's not necessarilly short - in some states (Russia, UK) life expectancy is expected to go down, because of various environmental and culture issues like alcohol abuse or widespread obesity.
Funny I just blogged about this the other day, on my blog Second Glance. I also came to the conclusion that I'd probably live longer than "expected" unless I drammatically change my lifestyle. It is the conditional that really makes life expectancy number useless for the individual.
I love the pristine optimism of this blog. Like newborn baby, wishing time would pass faster to get all those wonderful things awaiting him. The future will be shiny, incomparably better than today, globalization will make us all rich, immigration is paradise on Earth, we are going to live forever (or almost). And we are so smart and so modest.
Russian males are falling like flies at age 54 since the collapse of their social order. East Germans stopped having children. European life expectations are not growing and there are some areas of regression. Lets hope you are right.
Demographers don't "solve this problem by completely ignoring it". Demographers do huge amounts of work on projecting life expectancies. But when they quote statistics for purposes of international comparison, they need to do so on an objective basis which can be reconciled to observable facts, not to model assumptions.
This is like saying that economists solve the problem of the distinction between GDP and quality of life by ignoring it. Except that it's much more true for economists.
DD, long time see no wittier comment. J^0