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Equation 3 · Part 6 · How Demography, Migration, and Urban Futures Actually Work

addition

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

What this part means

Add the term after the plus sign to the term or group before it.

Its job in the formula

Add the term after the plus sign to the term or group before it.

The passage around this formula

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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Learn the underlying idea

Addition combines quantities; subtraction measures the signed difference between them. Parentheses show what is combined before the rest of the expression is evaluated.

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Sources cited in the surrounding passage

These citations provide research context; check each source for the exact claim it supports.