The dominant population (POP) equation is a simple addition of births (BIRTHS) at the bottom of the cohort distribution, subtraction of deaths (DEATHS) from each population cohort, and advance of people to the next cohort over time.
The following key dynamics are directly linked to the Dominant Relations:
Births are primarily a function of the total fertility rate (TFR), which in the longer term responds especially to education level of the adult population. The model user has direct control over TFR with a multiplier ( tfrm ), but also much control for low fertility countries with a parameter specifying long-term stabilization level and lower boundary for fertility ( tfrmin ). There is also a secular trend reduction in fertility (controlled by ttfrr ).
Deaths are primarily a function of life expectancy (LIFEXP), itself computed within the IFs health model where, like fertility, it responds in the long run to adult education and also to GDP per capita and technology change. The model user has direct control over all deaths with a mortality multiplier ( mortm ) and over those specific to a cause of health with an alternative multiplier ( hlmortm ). There is also a secular trend reduction in mortality (controlled by tmortr ).
The larger demographic model in combination with the health model provides representation of and control over migration; the fertility impact of infant mortality and contraception use rates; and the mortality impact of many factors including undernutrition, smoking rates, and indoor air pollution from open burning of solid fuels.