Life expectancy, or the average life expectancy of the population - a statistical measure indicating the number of the years, which on average is going to live generation born or peers at a certain level of age-specific mortality. This indicator attach great importance to the demographic statistics of the overall assessment of mortality. To gain in life expectancy are mortality tables (see) and life expectancy. Mortality tables give an idea about the procedure of extinction or survival of a certain number of births by age groups. For the original set of births is usually taken 100 000. Multiplying consistently the number of surviving to a specified age the probability of living until the next age, get the serial number of surviving, of which determine the values of life expectancy at each age. Compiled thus tables reflect the order survival is possible, provided that during the life of generations indicators of mortality by age of those years, associated with the compilation of tables. These tables can be calculated for each specific conditions, life expectancy of men, women, the population of some districts and cities, and so on, for Example, from the published CSO of the USSR data for 1958-1959 the average life expectancy of men in these years was equal to newborns 64,42 year, i.e., boys born in these years, had to live an average of 64, 42 years boys 5 years of age, life expectancy was 63,46 year, i.e. they had on average live another 63,46 year and all, therefore, 5+63,46=68,46 year; for men under the age of 30 years, life expectancy was equal 40,71 year, i.e. in total, each of them could on average to live 30+40,71 = 70,71 year, and so on
The concept of "average life" should not be confused with the concept of "average age living" or "the average age of the deceased". For example, the average age born 0 years, and the average life expectancy of 70 years.
The average length of life is not dependent on age-sex composition of the population, the level of birth rate, migration of the population. This index depends only on the level of mortality by age groups.

The average life expectancy of the population of the USSR and pre-revolutionary Russia (in years)
Years Life expectancy
total population men women
1896 - 1897
1926 - 1927
1958 - 1959
1968 - 1971
32
44
69
70
31
42
64
65
33
47
72
74

The difference in life expectancy of men and women depends on various mortality rate by age groups. The shown data evidences about the continuous improvement of health of the USSR in terms of the higher life expectancy.
Cm. Demographic, Sanitary statistics.

Life expectancy (or rather the life expectancy of the population) in the demographic and health statistics - the number of the years, which on average is going to live this generation born or peers certain age, provided that during their life deaths in each age group will be such what it was in that year being the year. This method of calculation P. W. adopted by the international statistical practice. Therefore calculated for different countries the average P. W. comparable.
The life expectancy should not be confused with the "middle age of the deceased and the average age of the living." The average age of the deceased is the sum of the years in the life of the dead, divided by their number. The average age of the living is the sum of the years past from birth to all living divided by their number. Both these indicators have no scientific value and are not suitable for the characteristics of the health of the population, depending not only on P. W., as from the age composition of the population. When increasing the birth rate, the average age and the living and the dead is reduced, with reduced birth rate increases. The same happens as a result of changes in the age structure of the population due to migration.
The life expectancy is obtained from the mortality tables (see) and Central P. W. For example, from the published CSO of the USSR mortality tables and the average P. W. the population of the USSR during the 1958-1959 shows that the average P. W. men in these years was equal to newborns 64,42 year, i.e. men born in the years had to live on average 64,42 years; for men the age of 5 P. W. was 63,46 year, i.e. they had on average live another 63,46 year and all, therefore, 5+63,46=68,46 years; for men, under the age of 30 years, the average P. W. equal 40,71 year, i.e. a total of every one of them may on average to live 30+40,71=70,71 year, and so on
To obtain the average life expectancy is necessary to estimate the mortality tables and the average P. W. The calculation of such tables is performed according to the census of population age-sex groups of the population and content on the age distribution of deaths over the years, adjacent to the year of the census, which defines the probability of living until a certain age. For the original set of births is usually taken 100 000. Multiplying consistently the number of surviving to a specified age the probability of living until the next age, get the serial number of surviving, of which determine the value of P. W. for each age. Designed tables reflect the order survival is possible, provided that during the life of the whole generation remained sanitary living conditions of those years, associated with the compilation of tables. Thus, published by the CSO of the USSR mortality tables of the population of the USSR in 1958-1959 indicate that if the sanitary conditions of life of the population remained unchanged (as they were in 1958-1959), the order of living until a certain age, P. W., the probability of death etc. would be as specified in the tables.
As actually living conditions and health status of population change, the mortality tables and the average P. W. characterize the sanitary condition only that place and those years or nearest to them, for which they are calculated. As changes over time living conditions of the population must compute the new tables of mortality and life expectancy. For practical purposes health ample summary mortality tables and the average P. W.
Indicators P. W. the most developed capitalist countries and their change for the past century is shown in table. 1. The increase P. W. over the last decade was achieved mainly due to the reduction of child mortality and reduce mortality from TB, acute infectious and other diseases that affect the population is predominantly in young and middle ages. In elderly and senile age, where the cause of death is most often are cardiovascular diseases and malignant tumors, P. W. compared with previous decades, increased slightly, as mortality from these causes is not reduced.
Economically marginalized capitalist countries, dependent countries and colonies have P. W. much lower than the developed capitalist countries.
The average life expectancy of the population of the USSR is shown in table. 2. In the USSR as a result of the huge social changes that occurred after the great October socialist revolution, been significant improvements in P. W. Compared to 1896-1897, are already in 1926-1927 P. W. increased by 12 years (from 32 to 44 years). In 1962-1963, the average P. W. reached 70 years, i.e. was 2 times more than in 1896-1897, and 1.5 times more than in 1926-1927 Especially increased average P. W. in women, free from domestic enslavement and got equal rights with men to work, leisure and education. With an average increase from 1896 -1897, P. W. in 1926-1927 from 32 to 44 years, i.e. by 38%, and in 1962-1963, up to 70 years, or by 119%, in women, the lengthening of the average P. W. respectively from 33 to 47 years, i.e. 42%, and up to 73 years, or 121 %, and men - from 31 to 42 years, i.e. 35%, and up to 65 years, or 110%. Successful implementation of plans for the construction of Communist society will lead to a further lengthening of the average P. W. population.
Cm. Demographic, Sanitary statistics.

Table 1. The average life expectancy (years)

Table 2. The average life expectancy of the population of the USSR (in years)