Demographics
Discussion
Lab Goals:
This module is for exploring "demographics", or age-structured human population growth.
The simulator includes a collection of countries with their current
populations and fertility and mortality rates. The simulator allows you to explore three
fundamental changes in these rates that alter
population growth.
- Shift childbearing to earlier or later in life.
- Change the fertility rates.
- Change the mortality rates.
The goals of this lab are:
- Explore those three rate changes.
- Understand how the same number of children per woman can lead
to different growth rates.
- Consider what different age structures mean to the people
who live in them.
User Interface
The display could use some explaining. A side-by-side pair of plot and "pyramid"
is one simulation. The bottom simulation runs the original data for
the country. The top runs a simulation with changed rates. The initial
difference between the two is a reproductive shift of 5 years (see the
change rates menu--a "step" is 5 years).
The reproductive rates
in the top simulation are shifted 5 years later than the original at the bottom.
Each pyramid base shows the country, year, current
growth rate, and average lifetime number of children per woman. Up the
middle are the age groups, or "cohorts". Males are on the left in blue, females on
the right in red/pink. For each age group there are two bars, one pale
and one bright colored. The pale bars show the original shape of the
pyramid, and the brights show the current simulation year. The "cohort"
aged 0-4 in year 2005 (the start) is highlighted in magenta. When they
reach reproductive age, their children are shown in lighter magenta.
So in this picture, year 2050, the starting cohort is now age 45-50, and
most of their children are age 10-30. The rest of the people age 10-30
are children of other cohorts.
By default, the simulator starts at year 2005 and stops when the bottom
cohort reaches the top. You can use the 
step
button to interrupt and proceed step-by-step, or to continue on past
the default stop year. 
Restart returns to year 2005.
Each plot
has two traces. The blue line is US Census International data, actual and projected, for
the country from 1950 to 2050. This projected line is exactly the same for the "original"
and "changed" simulations. The purple line is the current simulation. Beneath the
plot is a mouse tracker - as you run your cursor over the plot, the tracker reads the
cursor location.
There are a number of reasons why the simulated and projected traces don't match.
For one, the simulator is using constant fertility and mortality schedules,
except as explicitly changed via the change rates
menu. The Census projects
those rates to change, and also projects
immigration, which is left out of these simulations. For example, this plot is
paired with the pyramid above for Germany, original rates.
The purple simulated line goes with the pyramid. The US Census Bureau apparently believes
that fertility will rise, mortality fall, or expect heavy
immigration (likely all three), because the simulation shows Germany's population
falling more sharply than the official projection.
You can zoom the plot using
the mouse. Drag a box upward to zoom in on the area inside the box. Drag it downward
to zoom the whole area of the plot, into that box area. Simply clicking on the plot restores
the plot limits.
You can select a new country to simulate with the Scenarios menu at the top.
Only positive and negative integers should be entered in the
change rates menu.
Changes 2000 to 2005
This simulator was written in 2000, and updated in 2005, including
updating the country scenarios with the latest US Census DB data. Over the past
15 years or so, worldwide population projections have changed dramatically,
and are still changing.
Non-obviously, the projections are different for the past as well as the future -
there's a long lag time in data collection, and they adjust past estimates.
-
USA: Projection revised from 1990 on. By 2050, the official projection is
up 16 million from the projection of 5 years ago.
-
China: Projection revised from 1985 on. Shows to cohort 90+ now (used
to be 80+). China's population is projected to crest by about
2025, ten years earlier than projected in 2000.
-
Egypt: Projection revised (upward) from 1980 on. Fertility has decreased and shifted
to later in life, but perhaps not as quickly as they expected.
The official projection is up 14 million by 2050 from the
projection of 5 years ago.
-
Germany: Projection revised from 1995 on. Fertility has increased, but
Germany's population is shown topping out by 2010 now, ten years earlier
than projected in 2000. Immigration has probably decreased.
The projection is down 7 million by 2050 from the
projection of 5 years ago.
-
India: This is a major change. Projection revised
downward from 1975 on. It seems fertility
has shifted to later and lower more quickly than expected.
The projection is down 665 million people by 2050 - 2.175 billion in 2050 vs.
the 2.840 billion projected 5 years ago.
-
Italy: Projection revised negligibly from 1985 on. Fertility
has increased slightly.
The projection is up 5 million by 2050 from the
projection of 5 years ago, but it's still declining.
-
Mexico: Projection revised from 1975 on. Fertility
down a bit, but has not shifted in age.
The projection is down 5 million by 2050 from the
projection of 5 years ago.
-
Mortality: unfortunately, I didn't update the mortality rates, because
the data in the IDB is still quite old (~1980-1990).
Further Information
Suggested explorations are in
Explore.
Equations and implementation details are in
Details, and
outside readings and links in References, including a
link to the US Census International Database if you'd like to explore other
countries. Another page,
HIV/AIDS, discusses the effect AIDS has on
demographics in hard-hit countries.
Ginger Booth, revised March 2005, orig. December 2000, for
oswald.schmitz@yale.edu