4.1.12 Review Structure And Functioning Of Model
This model has a single stock (level or accumulator) POPULATION. By definition, it is a first-order problem. POPULATION:
- can grow through two mechanisms involving the physical flows of being born, that is, Birthing and Migrating-in from somewhere else to live in Charmville; and
- can decline through two mechanisms involving Dying or Migrating-out.
Dependencies within the model are:
- Birthing depends on size of POPULATION, as indicated by the information arrow from POPULATION to Birthing: the greater the population, the greater the number of children born each year (for a given fraction of child-bearing age females in the population, and similarly for a smaller population).
- Dying depends on size of POPULATION, as indicated by the information arrow from POPULATION to Dying: the greater the population, the greater the number of people who will die each year (and similarly for a smaller population).
Note that this model only considers changes in the total population without consideration age-groups within the population. That is, for simplicity, it does not categorise demographic groups. That can be accommodated in a more-sophisticated array model where dimensions within the array might be used to capture age-groupings.