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Equation 4 · Part 7 · Demography, Migration, and Urban Futures in Practice: An Advanced Technical Guide

addition

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

Aging the cohort forward. For each one-year (or five-year) step, every age-sex cohort is advanced by applying an age-specific survival ratio — the probability of surviving from one age to the next, derived from a life table built out of registered deaths and mortality schedules — and then subtracting deaths and adding net migrants assigned to that same age and sex [ 1 ] . Symbolically, for a cohort of age a and sex s in year t : Pa+1,s,t+1=Pa,s,t⋅Sa,s,t+Ma,s,tP_{a+1,s,t+1} = P_{a,s,t} \cdot S_{a,s,t} + M_{a,s,t}. where P is the population count, S is the age-and-sex-specific survival ratio for that interval, and M is net migration assigned to that cohort during the interval. The youngest cohort in each step is not aged forward from an existing cohort; it…

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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

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