# Life expectancy

The word "life expectancy" and with the addition of the adjective "middle" very often misleading all those who are not familiar with the exact scientific value of this term. You have to remember that it does not correspond to the life expectancy, which could be a person, if its existence were excluded all factors that reduce the life. "The average duration of life" - the term is purely statistical, even - math. It was the result of an accurate count of how many years can expect people to survive in each country and in each given period in a particular age. The calculation is made only on the basis of accurate statistical data on the age structure of the population, mortality in each of the ages, the number of people living in each age group. All these data are population censuses, and the accuracy of their matches exactly produced by the census.
Just another idea is the phrase "biological life span". This notion that we have not put an exact idea, as yet do not know exactly how long the human body can live in the most favorable conditions. We do not and can not be for that accurate statistical data. To do this, we can not proceed from the results of the census, and from data on life expectancy of individuals, when it is precisely established. For example, the famous Russian microbiologist S. Vinogradsky was born in 1856 and died and 1953. Therefore, he lived 97 years, it will be a biological duration of his life. But these figures do not answer the question of whether it is the normal duration and destination for human life. They show only that person can, in certain circumstances, to live up to 97 years, or up to one hundred.
But is this the life expectancy of biological limit it at all, can all the people or the vast majority of them under favorable conditions to live to that age? To this question we cannot give an exact answer, we can only assume. But the larger the number of people for whom it was possible to establish precisely the dates of birth and death, live to that age, the more we have reason to suppose that human life is not limited to 70-75 years, and can last much longer.
We consistently let us, therefore, two problems: the problem of life expectancy, the issue exact, clear, based on mathematical calculations, and the problem of life expectancy, based on assumptions on the data about some of the people that lived to a high age.
Meanwhile, very often in the press, in Newspapers, in the wide circles of the population both of these very different concepts confused. Therefore, it is necessary to give some idea of how to determine the life expectancy in the country in a given year. But here we simplify this concept, we will give only the basic elements of its calculation, leaving aside all accurate mathematical calculations.
Suppose that you were born a generation of people by number 100 000. This generation will live and develop, but each year it will drop as a result of death, all new and new faces. The data records of the registry office show how many people died in each calendar age every year, in other words, give the age mortality. For example, in children during the first year of life died on 1000 person of 200, therefore, in this year the man had 200 chances of 1000 die in the first year of life and 800 chance to survive to the next year. But not all died, reaching one year of age. Many died at the age of several months. Therefore, you can roughly be seen to be dead within the first year of life half reaches the age of one year.
Suppose that at the age from one to two years died 100 children, therefore in this age, the child was, on average, 100 chances of 1000 die and 900 chances (OO-100) to survive.
The same calculation can we do and for all subsequent ages. Therefore, knowing how many people died in each given age - years of life,we can know how many people survived that long.
Now add up all the years people of the same generation. For this purpose it is necessary for each age group to multiply the number of persons with this age, on the number of years. So, if at the age of 70 years from the people of this group has remained is alive 150, the number of years of their will 150X70 - 10500. This calculation can be done for each age group. With all of this data will provide the total number of years lived by all people of this generation.
To get the average lifetime of this generation have received sum is divided by the accepted us in this case the number of this generation, that is 100 000. This figure will be called average life expectancy of this generation in a given year.
Here we are extremely simplified calculation of this magnitude, but this is enough to understand its meaning. As we see, it is the value of a purely abstract, mathematical.
Therefore, the value of the average life expectancy is determined only age-specific mortality and survival. It does not depend on the age structure of the population.
From this it follows that the average life expectancy is calculated in this way will be the less, than there will be more deaths in one of ages.

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