3333glossary * R *
Demographical and statistical terms  Symbols 
rate computation the crude birth, death, marriage, divorce etc. are generally the annual number of each of these vital per 1000 midyear population. 

rate of population growth the increase or decrease of a population in a period divided by the number of personyears lived by the population during the same period. 
r or TA 
rate of natural increase at time t, or b(t)d(t) the difference between the births and deaths occurring during by the number of personyears lived by the population during the same period. This rate, which specifically excludes changes resulting from migration, is the difference between the crude birth rate and the crude death rate. 
n(t) 
replacementlevel fertility the level of fertility at which a cohort of women on the average are having only enough daughters to replace themselves in the population. By definition, replacement level is equal to a net reproduction rate of 1.0. The total fertility rate is also used to indicate replacementlevel fertility. Generally, in industrialized countries, a TFR (total fertility rate) of 2.1 is considered to be replacement level. 

reproductive histories are accounts obtained for individual women of the important events in their reproductive lives, such as marriages, pregnancies, births, infant deaths, etc., and their dates. Reproductive histories are often obtained retrospectively from surveys. 

resistance function is the mathematical expression of the resistance data computed on the lifetable. 
r(x); 
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