Life expectancy

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Bert | 01:33 Mon 13th Nov 2006 | Science
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When people say that the life expectancy of a man in this country (UK) is 79 (or whatever it is), what does it mean?
It surely cannot mean that a boy born today will have a 50/50 chance of living to 79, because we have no idea what medical advances may be made in the next 79 years that may increase the life expectancy, not do we know if some plague is around the corner which will reduce it, as HIV/AIDS has reduced life expectancy in Africa. How is this statistic arrived at ? (Please do not bother to reply with a guess if you know nothing about it.)


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o.k then, but I suspect all you're going to get is guesses.
It's the average age people die.

In the time it took you to write your question you could have simply googled "life expectancy definition" and got a comprehensive answer such as:

The life expectancy you refer to is, roughly speaking, a simple average based on available data: If 1000 people die you add up their age and divide by 1000 to get an average person. Life assurance companies carry more accurate figures based on various important factors including: gender, lifestyle (smoke, drink, socio-economic group), genetic history, medical history, etc. They can then take an informed guess of an individuals life expectancy and set policy rates accordingly
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Thanks, Dawkins. You are quite right. I have expressed my amazement occasionally when people put questions to Answerbank like "Where is Albania?". I guess I was hoping for a simple explanation, and I thought my extra thoughts about how future events might affect life expectancy would provoke some discussion.
Would you agree that life expectancy must be historical, then? That is we can only say that the life expectancy for someone born in 1927 was 79? This figure must have been greatly influenced, for men at least, by living through the Second World War (or not, as the case may be). Or can the figures be manipulated so that we can forecast the life expectancy of someone born in any year since 1927? A male born in 1946 would have a life expectancy greater than 79 years, probably, but we won't know until 2025.

I truly apologize, Bert, for being rude enough to offer a guess but, my guess is that your premise is flawed. When one gives a life expectancy today, it is not of how long they will live but how long those who died today have already lived. Conclusions drawn from this number are open to anyone's discretion.
I know nothing about it but I will answer anyway seeing as there is nothing you can do about it.

You use the term "Life expectancy" as if there is a single standard method for arriving at a figure, this is not the case. Many different models exist, some do try to account for medical advances, some disregard infant mortalities as these can skew the figures, some are the average age people die at today, some mean the average age a person will live to if born today, yada yada yada.

In answer to your question you need to ask the person saying "Life expectancy" what particular formula they are using and you will have your answer.
I haven't bothered to read up, but based on the answers posted already I would try to explain it like this:

If I use the same example as you, a male born in the UK in 1927, dying today would; probably have the age of 79 (unless he was born after 13th November). At the time of WW2, other people born in 1927 would be teenagers, an age group that I imagine would usually have a very low death rate. However, the conflict would lead to many more teen deaths than in an uneventful period. The effect of so many teen deaths would have dramatically lowered the life expectancy of this time.

However after the war ended and so many young people stopped dying, the life expectancy would start to rise again. All the teens who survived the war would be subject to this new life expectancy. That is to say you are always subject to the current life expectancy regardless of when you are born.

This does not mean that the you will live to this age and not beyond as it is an average and is not applicable to individuals. If the life expectancy is constantly changing it will, as you say, reflect changes such as particularly virulent diseases, war, medical advances, etc.

Low life expectancy usually reflects a high infant mortality rates rather than mature adults dying at a young age (war/genocide are exceptions). Male life expectancy is generally lower than female life expectancy due to the dangerous nature of male employment such as space exploration and bull fighting.

I am 85 and as I have passed the dreaded 79 years life expectancy, for me there seem to be no limit. David Freeman..

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