glossary * D *
Demographical and statistical terms  Symbols 
death is the permanent disappearance of all evidence of life at any time after live birth has taken place ( post natal cessation of vital functions capability of resuscitation ). This definition therefore excludes foetal deaths. 

deaths at age x represents the number of deaths from age zero and exact age x observed in the life table. 
D(x) 
deaths at age exact x are given by the first derivative of the life function 
d(x) 
deaths between ages x and age x+n deaths calculated by the difference between survivors of the life table of age x and of age x+n 
d _{x,x+n} 
death rates by causes are the annual number of deaths in each cause group reported for the year per the corresponding midyear population. 

delivery is called the actual process of expulsion of the foetus. 

demographic model consists of a theoretical construct representing the evolution of a population(of individuals, couples, families, households, etc.) and its structure on the basis of its initial state and the effect of various demographic variables (such as fertility, fecondability, mortality, etc.). In a static model these variables remain constant; in a dynamic model these variables are allowed to change over time. 

demographic transition the historical shift of birth and death rates from high to low levels in population. The decline of mortality usually precedes the decline in fertility, thus resulting in rapid population growth during the transition period. 

density of population is the number of person in a year total population per square kilometre of total surface area of a country. 

dependency ratio persons aged 014 and over 65 of given sex per person 1564 of given sex 
ID 
developed (or more developed) countries countries that have higher levels of per capita income, industrialization and modernization. 

developing (or less developed) countries countries that have lower levels of per capita income, industrialization, and modernization. 

direct methods systems of linear algebraic equations can be solved either by direct methods or by iterative methods. For system of moderate size, the useof direct methods is often advantageous. 

distribution of population at age x
is the ratio of the population of age x, x+n to total population 
C(x) 
divorce is a final dissolution of a marriage, that is, that separation of husband and wife which confers on the parties the right to remarriage under civil, religious and/or other provisions, according to the laws of each country. 

dizigotics twins are due to the simultaneous fertilization of two or more ova and the resulting children may be different sexes. 

Dwelling unit is a statistical abstraction denoting housing accomodation appropriate for occupation by one household. 
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