The Demographic Transition Model

You’ll be able to

Describe the birth rates, death rates, and growth in each DTM stage
Calculate natural increase rate and doubling time from vital rates
Apply the Epidemiologic Transition and evaluate the model’s limits

The five stages

The Demographic Transition Model (DTM) traces how birth and death rates change as a society develops. Stage 1 (low growth): high birth rate, high death rate — pre-industrial societies; no country is here today. Stage 2 (high growth): death rate plunges thanks to better food, sanitation, and medicine while births stay high, so population explodes (Sub-Saharan Africa, e.g. Niger). Stage 3 (moderating growth): birth rate falls as families urbanize and women gain education and work (Mexico, India). Stage 4 (low growth): low birth and death rates, near-stable population (United States). Stage 5 (declining): birth rate drops below death rate, so population shrinks and ages (Japan, Germany, Italy).

Natural increase and doubling time

A population’s growth from births and deaths alone is the Natural Increase Rate (NIR) — the crude birth rate minus the crude death rate, expressed as a percent (migration is excluded). A positive NIR means growth; a negative NIR (Stage 5) means decline. From the NIR you can estimate doubling time — the years for a population to double — with the Rule of 70: divide 70 by the percent growth rate. A 2% NIR doubles a population in about 35 years, showing how even modest percentages compound dramatically.

Natural increase & doubling time

NIR (%) = (CBR − CDR) / 10 doubling time ≈ 70 / NIR(%)

Crude birth/death rates are per 1,000 people, so dividing their difference by 10 converts to a percent. The Rule of 70 then estimates years to double. NIR ignores migration.

The Epidemiologic Transition

Riding alongside the DTM is the Epidemiologic Transition, which describes the changing causes of death as a society develops. Early stages are dominated by infectious and parasitic diseases and famine; as countries advance, deaths shift toward chronic and degenerative diseases of older age — heart disease, cancer. A proposed later stage warns of the re-emergence of infectious disease through antibiotic resistance and rapid global travel, reminding us that transitions are not guaranteed to be one-way.

Worked example

A country has a crude birth rate of 34 per 1,000 and a crude death rate of 10 per 1,000. Find its natural increase rate, estimate its doubling time, and identify its likely DTM stage.

1.NIR = (CBR − CDR) ÷ 10 = (34 − 10) ÷ 10 = 24 ÷ 10 = 2.4%.
2.Doubling time ≈ 70 ÷ 2.4 ≈ 29 years.
3.A still-high birth rate (34) with a sharply lowered death rate (10) and rapid growth matches Stage 2 of the DTM.
4.Such a country would show a wide-based population pyramid and face pressure to expand schools and jobs.

Answer: NIR = 2.4%, doubling time ≈ 29 years, and the country is in Stage 2 — death rates have fallen while births remain high, driving rapid growth typical of the mortality decline that opens the transition.

Checkpoint

Which change is the primary driver of the dramatic population growth that marks the move from DTM Stage 1 to Stage 2?

Watch out

NIR uses only births and deaths — it excludes migration. A country can have a low NIR yet still grow quickly from immigration (or shrink despite a positive NIR through emigration). Do not fold migration into the NIR calculation.

Checkpoint

A wealthy country now records a birth rate below its death rate and a rapidly aging population. Which DTM stage and consequence best fit?

Answer the 2 checkpoints as you read.