From: Dr. Ed G (Avatar) 1/11/99 20:22:01 Subject: What does life expectancy mean? post id: 4186 Average life expectancy for an Australian woman is about 79 years. What does life expectancy really represent? Can anyone tell me how it is worked out? I can think of a few ways that could give an answer. Firstly, you could simply find the average age of every woman who died last year, but this would bias the result towards the past. Secondly, you could work out the percentage of zero year olds who didn't make it to one, the percentage of one year olds who didn't make it to two etc, assume that these statisitics were static, calculate the percentage you expect to live to each age, differentiate, and find the mean of this function. It would give a "present" figure of average age, but it would be hard to say to whom it applied. Thirdly, and in my view most meaningfully, you could give the expected lifespan of someone being born now. To do that, you would need to know (or estimate) not how many people of age 19 don't make it to 20, etc, but how many people who will be aged 19 in 2018 won't make it to 20, etc. Presumably this value will be higher, and the total average lifespan will be greater. The advantage with this method is that you at least know what the figure means: the expected (mean, I presume) lifespan of someone being born right now. The disadvantage is that you have to make projections about health and safety in the future. Can anyone tell be how the published life expectancies are really calculated? 8^) From: Dr. Ed G (Avatar) 1/11/99 23:16:52 Subject: re: What does life expectancy mean? post id: 4204 Personally, I rather see the life span distribution than a single number which could be meaningless. I'd be very interested to see where the peaks are. For example, the reason the lifespan seems to have drastically increased over the last 50-100 years in the Industrialised world has more to do with drastic reductions in child mortality than an increase in the age to which people live, per se. If you were to calculate life expectancy only from those who'd reached 50 years of age, then the average life expectancy in the West since WWII has only increased by about 5 months. Hardly anything for Modern Science to get excited about (although it is responsible for drastic improvements in nutrition which is one of the principle factors, as I understand it, in the reduction of child mortality). Soupie twist, Ed G. From: steve(primus) 2/11/99 6:48:31 Subject: re: What does life expectancy mean? post id: 4227 As far as I can ascertain, average life expectancy is the average of the age at death. This is a rather meaningless figure as it includes child mortality. More useful figures are the life expectancy at certain ages. If you reach 20, what is the probability that you will reach 50, if you reach 50 what is the probability that you will reach 70 etc. At birth, the probability of making 80 might be, say, 2% but if you make it to 60, the probability might be 30% and at 70 maybe 50%. Life expectancy increases as you reduce child mortality so societies with an increasing life expectancy are those where fewer people die young. Even in societies with a low life expectancy, if you make it through the dangerous years, you can expect a long life. From: Mike Langford 2/11/99 22:36:07 Subject: re: What does life expectancy mean? post id: 4444 Good calls, Dr Ed G and steve(primus). I wonder how the median lifespan has changed. I found this http://www.ac.wwu.edu/~stephan/drl/drl.lifetable.html West Washington Uni page, which gives reasonable instructions for calculating life expectancy at any age. If I am interpreting it correctly, my model 2 was the closest, meaning that the life expectancy is calculated on the assumption that the precentage of people who die between x and x+n does not, itself, change over time. This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.