AP Syllabus focus:
‘The demographic transition is typically shown using a four-stage demographic transition model (DTM) based on changes in birth and death rates.’
The four-stage demographic transition model (DTM) explains how a country’s population changes as it develops, focusing on shifting birth rates and death rates and the resulting patterns of population growth.
Core idea: how the DTM is built
The DTM tracks population change using two rates across time: birth rate and death rate.
Schematic demographic transition model showing how death rates typically fall first, followed later by declining birth rates. The changing vertical separation between the two curves visualizes when population growth accelerates (large gap) versus slows or stabilizes (small gap). Source
The gap between them determines whether population size grows quickly, slowly, or stabilises.
Demographic transition model (DTM): A four-stage model that shows how birth rates and death rates typically change as a society develops, shaping overall population growth.
Because the DTM emphasises “typical” patterns, it is a general framework rather than a perfect timeline for every country.
Crude birth rate (CBR) / crude death rate (CDR): The annual number of births or deaths per 1,000 people in a population.
The four stages (birth and death rate patterns)
Stage 1: High stationary
Birth rate: high
Death rate: high
Population growth: low overall (rates roughly offset)
Common constraints include limited medical care and sanitation, and variable food supply, keeping mortality high and incentivising high fertility.
Stage 2: Early expanding
Birth rate: remains high
Death rate: drops rapidly
Population growth: rises sharply (large gap between CBR and CDR)
A falling death rate is commonly linked to improved public health (clean water, sanitation), better food availability, and basic medical advances, while social norms and access to contraception may lag behind.
Stage 3: Late expanding
Birth rate: declines significantly
Death rate: continues to decline or stabilises at a low level
Population growth: slows (narrowing gap)
Birth rates often fall with greater access to family planning, changing economic incentives (higher cost of raising children), increasing urbanisation, and expanded education and employment options.
Stage 4: Low stationary
Birth rate: low
Death rate: low
Population growth: near zero (rates roughly equal at low levels)
Total population size may stabilise, though population momentum can continue if a large cohort is entering reproductive ages.
Reading and applying the DTM correctly
The model’s key output is the relationship between birth and death rates, not a fixed number of years per stage.
The steepest population increase typically occurs in Stage 2, when death rates fall faster than birth rates.
Five-stage demographic transition model diagram plotting birth rate, death rate, and total population across development stages. The graphic makes it easy to see why population size rises most quickly when death rates drop rapidly while birth rates remain high, then slows as birth rates decline. Source
The DTM helps predict pressures on resources and services:
Rapid growth phases can strain housing, water supply, schools, and jobs.
Later stages often shift needs toward ageing populations and long-term healthcare planning.
FAQ
Countries can experience conflict, policy shifts, pandemics, or uneven development, causing birth/death rates to change out of sequence or at different speeds than the model suggests.
Yes. Rapid adoption of healthcare or contraception, or strong government interventions, can compress transitions so Stage 2 and Stage 3 changes occur over a short period.
High immigration can raise population size even when birth and death rates are low. Emigration can reduce growth despite a large birth–death gap, complicating stage identification.
Even with low birth rates, a large cohort entering reproductive age can keep total births relatively high for a time, delaying stabilisation of total population size.
CBR/CDR are averages and don’t show age structure. Two countries with identical CBR/CDR can have different growth trajectories if one has many young people and the other is ageing.
Practice Questions
Describe how birth and death rates change from Stage 2 to Stage 3 in the four-stage DTM. (2 marks)
Death rate is low/stabilises or falls slowly (1)
Birth rate declines markedly (1)
(6 marks) A country shows a rapidly falling death rate while its birth rate remains high.
(a) Identify the DTM stage most consistent with this pattern. (1)
(b) Explain two reasons death rates might fall before birth rates. (4)
(c) State one effect this gap has on population growth. (1)
(a) Stage 2 / early expanding (1)
(b) Any two explained, e.g. improved sanitation/clean water reduces infectious disease (2); improved food supply/nutrition reduces mortality (2); basic medical care/vaccination reduces deaths (2) (max 4)
(c) Rapid population growth / high natural increase (1)
