glossary * I *
Demographical and statistical terms  Symbols 
incidence rate is the number of persons who contact
a specific illness or disease during a 

infant mortality is the mortality of live born children who have not yet reached their first birthday. 
Q(0) 
infant mortality rates are the annual number of deaths of infants under one year of age per 1000 live births in the same year. 

infecundity is the lack of the capacity of a men, a woman or a couple to produce a live birth. 

instantaneous death rate is the limit of the _{n}q_{x }values (or probability at age x of dying before reaching age x+n) as n tends to zero. 
m (x ) 
intercensal estimates relate to dates intermediate to two or more censuses, and take the results of these censuses into account. 

intrinsic birth rate the true or intrinsic birth rate is the birth rate that would eventually be reached in a population subject to fixed fertility and mortality schedules. It is the birth rate of stable population. 
b 
intrinsic death rate the true or intrinsic birth rate is the death rate that would eventually be reached in a population subject to fixed fertility and mortality schedules. It is the death rate of stable population. 
d 
intrinsic rate of natural increase is the rate computed by Lotka who proved (1925) that a closed population with constant agespecific fertility and mortality schedules would eventually have a constant rate of natural increase. This rate has also been called "true rate of natural increase", or "implicit rate of natural increase". 
r 
iterative methods systems of linear algebraic equations can be solved either by direct methods or by iterative. Iterative methods are used primarily for solving large and complex problems for which, because of storage and arithmetic requirements, it would not be feasible or it would be less efficient to solve by a direct method. 
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