← All parts of this equation

Equation 3 · Part 4 · How Demography, Migration, and Urban Futures Actually Work

Symbol M_a,t

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

What this part means

net migration entering or leaving that age group during the interval.

Its job in the formula

MaM_a,t is one of the signed contributions combined to compute the quantity on the left.

Where the article explains it

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 migration entering or leaving that age group during the interval.

The passage around this formula

…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 migration entering or leaving that age group during the interval. Births are generated separately by summing age-specific fertility rates across women of childbearing age, then applying infant survival to place the new cohort at age zero the following year. Iterating this recursion…

Read this part in the article →

Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

Open the illustrated subscripts: which member of a family? guide →

See this notation across published equations →

Sources cited in the surrounding passage

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