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Births, deaths and migration (cont.)
The Balancing Equation
These principles are brought together by the Balancing Equation. The Balancing Equation expresses the way in which any population changes over time, and shows how population stock is connected to population flow.
P (t + n)= P(t) + B – D + I – E
Where:
- P(t) = Population at time t
- P(t + n) = Population at time (t + n), where n is the length of the interval
- B = Births
- D = Deaths
- I = Immigration
- E = Emigration