IBEnvironmental Systems & Societies (ESS)DPSLRevision NotesHuman Systems & Resource UseHuman Population DynamicsDemographic Variables

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Last exams 2025

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Demographic Variables (DP IB Environmental Systems & Societies (ESS))

Revision Note

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Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

Demographic Variables

  • Demographic tools are essential for understanding and quantifying human population dynamics

    • They provide valuable insights into birth and death rates, fertility patterns, population growth rates, and other demographic indicators

  • Below are some key demographic tools and how they are calculated:

Crude Birth Rate (CBR)

  • The CBR is the number of live births per 1 000 individuals in a population during a specific time period

  • It is calculated by dividing the total number of live births in a year by the total population and then multiplying by 1 000

CBR=total number of live births per yeartotal population×1 000

Worked Example

A country has 25 000 live births in a year, and the total population is 500 000.

Calculate the crude birth rate.

Answer

CBR = (Number of live births / Total population) x 1 000
CBR = (25 000 / 500 000) x 1 000
CBR = 50 births per 1 000 individuals

Crude Death Rate (CDR)

  • The CDR is the number of deaths per 1 000 individuals in a population during a specific time period

  • It is calculated by dividing the total number of deaths in a year by the total population and then multiplying by 1 000

CDR=total number of deaths per yeartotal population×1 000

Worked Example

In a given year, a country recorded 15 000 deaths, and the total population is 750 000.

Calculate the crude death rate.

Answer

CDR = (Number of deaths / Total population) x 1 000
CDR = (15 000 / 750 000) x 1 000
CDR = 20 deaths per 1 000 individuals

Total Fertility Rate (TFR)

  • The TFR is an estimate of the average number of children a woman would have during her reproductive years if she experienced the current age-specific fertility rates throughout her lifetime

  • It is calculated by summing the age-specific fertility rates (ASFR) and multiplying the result by five

TFR=ΣASFR×5

Worked Example

The age-specific fertility rates for a country are as follows:

Age 15-19: 20 births per 1 000 women
Age 20-24: 80 births per 1 000 women
Age 25-29: 120 births per 1 000 women
Age 30-34: 100 births per 1 000 women
Age 35-39: 40 births per 1 000 women
Age 40-44: 10 births per 1 000 women

Calculate the total fertility rate.

Answer

TFR = (20 + 80 + 120 + 100 + 40 + 10) x 5
TFR = 1 850 births per 1 000 women

Doubling Time (DT)

  • The DT is the time it takes for a population to double in size based on its current growth rate

  • It is calculated using the rule of 70, where the number 70 is divided by the population growth rate

DT=70growth rate %

Worked Example

A population has a growth rate of 2% per year.

Calculate the doubling time.

Answer

DT = 70 / Growth rate
DT = 70 / 2
DT = 35 years

Natural Increase Rate (NIR)

  • The NIR is the rate at which a population grows or declines due to the difference between the crude birth rate and the crude death rate

  • It is calculated by subtracting the CDR from the CBR and then dividing the result by 10

NIR equals fraction numerator CBR minus CDR over denominator 10 end fraction

Worked Example

A country has a CBR of 25 births per 1 000 individuals and a CDR of 10 deaths per 1 000 individuals.

Calculate the natural increase rate (annual growth rate).

Answer

NIR = (CBR - CDR) / 10
NIR = (25 - 10) / 10
NIR = 1.5%

  • These demographic tools provide valuable quantitative measures to analyse and compare population trends across different regions and time periods

  • They assist policymakers, researchers, and demographers in understanding population dynamics, projecting future growth, and formulating effective strategies for social and economic development

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    Author
    Reviewer
    Alistair Marjot

    Author: Alistair Marjot

    Expertise: Biology & Environmental Systems and Societies

    Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

    Bridgette Barrett

    Author: Bridgette Barrett

    Expertise: Geography Lead

    After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.