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Pa+1,t+1=Pa,t Sa,t+Ma,tP_{a+1,t+1} = P_{a,t}\, S_{a,t} + M_{a,t}

Why this formula appears here

The UN Population Division builds its projections using the cohort-component method : rather than extrapolating total population, it starts from the population by single year of age and sex in a base year, and ages every cohort forward one year at a time by applying age-specific and sex-specific survival probabilities (mortality), age-specific fertility rates applied to women of reproductive age (which generates the next year’s births), and net international migration assumptions applied by age [ 1 ] . Formally, for an age group a in year t : Pa+1,t+1=Pa,t Sa,t+Ma,tP_{a+1,t+1} = P_{a,t}\, S_{a,t} + M_{a,t}. where Pa,tP_{a,t} is the population in age group a at time t , Sa,tS_{a,t} is the survival rate applied to that cohort, and Ma,tM_{a,t} is net…

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Pa+1,t+1P_{a+1,t+1}

Symbol P_a+1,t+1

PaP_a+1,t+1 is part of the quantity the equation computes from the expression on the right.

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Published contexts (1)

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Pa+1,t+1=Pa,t Sa,t+Ma,tP_{a+1,t+1} = P_{a,t}\, S_{a,t} + M_{a,t}

Equation 3 · Human Systems

How Demography, Migration, and Urban Futures Actually Work

This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.

The UN Population Division builds its projections using the cohort-component method : rather than extrapolating total population, it starts from the population by single year of age and sex in a base year, and ages every cohort forward one year at a time by applying age-specific and sex-specific survival probabilities (mortality), age-specific fertility rates applied to women of reproductive age (which generates the next year’s births), and net international migration assumptions applied by age [ 1 ] . Formally, for an age group a in year t : Pa+1,t+1=Pa,t Sa,t+Ma,tP_{a+1,t+1} = P_{a,t}\, S_{a,t} + M_{a,t}. where Pa,tP_{a,t} is the population in age group a at time t , Sa,tS_{a,t} is the survival rate applied to that cohort, and Ma,tM_{a,t} is net…

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