Mapping the Stock and Flow Structure of Systems

Representing Stock and Flow Networks

A. (10 points Population Demographics.

Imagine a small town in rural Kansas with 3000 inhabitants. The population is initially evenly distributed between children aged 0 to 20 years, child-bearing adults aged 20 to 45 years, and seniors aged 45 to 75 (assume that no one lives past age 75). In its marital relations, the town is quite typical; when two people are married, they have, on average 2 children together. You are interested in studying how the demographics of the small town will change over time. You can assume for the purpose of this model that all deaths are related to old age.

The model will contain the elements listed below. Identify each element as either stock, flow, or auxiliary, and label its units. For each stock, determine its inflows and outflows. Add all flows and causal/information links.

maturing rate

years as a child-bearing adult

children

number of child-bearing couples

death rate

years as a child

aging rate

birth rate

seniors

babies per couple

child-bearing adults

adults per couple (including this as an explicit variable can help some, others may implicitly incorporate it in other variables)

Years as a senior

total population (sum of the populations of all age groups)