Because the unit cumulative net growth rate = (first-stage net growth rate+1)× (second-stage net growth rate+1)× intermediate quantity× (last-stage net growth rate+1)× (current net growth rate+1) Therefore, the ratio of new increment to net increment can be expressed as the data growth rate of n years = [the sum of intermediate times (1(n-1))-1] ×100%.
Net increase refers to the difference between the increased quantity and the consumed or lost quantity. Net population growth is the sum of natural population growth and immigration growth. Changes caused by birth and death are called natural population changes, and population growth caused by natural population changes, that is, population growth caused by birth offsetting death, is called natural population growth.