glossary    * S *
Demographical and statistical terms Symbols
sex ratio
is the ratio between males and females (or vice versa) of a population.
sex ratio at birth
is the ratio between male births and female births (or vice versa) of a observed population.
sex structure
of the population is measured by the ratio of the total number of one sex to the total number of the population.
short-term emigrants
are residents or persons who have resided continuosly in the country for more than one year, who are departing to work outside the country for one year or less, and their dependants including domestic employees.
skewness of a fertility distribution
represents the degree of asymmetry of a function or a curve of the age-specific rate of fertility
spontaneous abortion
abortion following a non-induced intra-uterine death, which may has occurred some time before expulsion.
stable population
a population with an unchanging rate of growth and an unchanging age composition, because age-specific birth and death rates have remained constant over a sufficient period of time.
standardized birth rates
to compare the fertility of different populations, standardized birth rates are often used to eliminate the effect on the birth-rate of certain differences in structure of the population (most commonly the age and sex structure).
stationary population
number of person-years lived between age x and x+n by an original cohort of 100,000 for a population with 100,000 annual births and deaths, or stable population in which the intrinsic rate of natural increase is zero.
L(x) or n L x
is so called the lack of the capacity of a men, a woman or a couple to produce a live child. Among women we distinguish primary sterility where the women ha never been able to have children, and a secundary sterility, which arise after one or more children have been born.
survival rates
survival rates are calculated from the stationary population as the ratio of the number of survivors in an age interval to the number in the preceding interval.
h SR x
surviving function
is the mathematical expression of the survivors of a life-table
number of survivors at age x out of an original cohort of 100,000 births.
lx or S x

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