| The Rate of Natural Increase (RNI) is
calculated by subtracting the CDR from the CBR. You can "see" this
relationship in the Demographic Transition Charts. The vertical "space"
between the CBR line and the CDR line is "natural increase." It can
either be express as a % rate (per 100) or a per 1000 rate. This rate
measures the speed with which a population is growing (or shrinking) as a
result of an excess of births over deaths. |
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| Examining the Rate of Natural Increase
Chart allows you to compare this "speed" in your populations. The Rate of
Natural Increase does not take into account migration, so the actual
population could be growing at a greater or lower level than that
indicated by the RNI. |
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| Remember, the Rate of Natural Increase does not take into account
migration, so the actual population could be growing at a greater or lower
level than that indicated by the RNI. |
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The Annual Rate of Population Growth does take migration
into account and is the actual rate of population growth that each
population
has experienced. Therefore by comparing the Rate of Natural Increase
with the Annual Rate of Population Growth you can determine whether net
in-migration or net out-migration was occurring at each time period. |
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If the Rate of Natural Increase is greater than the Annual
Rate of Population Growth, then net out-migration is occurring. This means
that the population is actually increasing at a rate less than it would
have if just fertility and mortality were affecting growth -- it means
that people must be migrating out of your population. If the Annual
Rate of Population Growth is higher than the Rate of Natural Increase -
then net in-migration is occurring. Greater numbers of people must be
entering into your population than leaving it. |
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The Net Migration Chart actually graphs the differences
between the RNI and PGR and thereby gives an estimate of net migration per
1,000 population. A negative number means the there is net emigration and
a positive number means that there is net immigration.. |
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