OFFICIAL STATISTICS SPECIALLY DESIGNED FOR INDIAN STATISTICAL SERVICE (ISS) AND OTHER GOVERNMENT & PRIVATE SECTOR STATISTICAL EXAMINATIONS
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Population projections estimate the future size and composition of a population under specified assumptions about fertility, mortality and migration. They are important for planning schools, health services, labour markets and infrastructure.
1. What is a population projection?
A population projection is a statistical estimate of future population under an explicitly stated set of demographic assumptions. It is not a prediction that must occur; the resulting figures depend on the assumptions and the period for which the projection is prepared.
ISS questions on official statistics often test definitions, statistical units, denominators, rates, index concepts and interpretation of published data. Focus on the exact meaning of each indicator before applying a formula.
2. Cohort-component method
The cohort-component method follows population cohorts by age and sex. Each cohort is updated using assumptions about survival, fertility and migration. The method is especially useful because it produces a structured population by age and sex rather than only a single total.
Future population estimate conditional on specified assumptions.
Population group classified by age and sex and followed through time.
Component determining how many members of a cohort remain alive.
Population change arising from movement into or out of an area.
3. Fertility, mortality and migration assumptions
Fertility assumptions determine the number of births, mortality assumptions determine survival, and migration assumptions account for additions or losses through migration. Changes in any one component can materially alter the projected population.
Always identify the numerator, denominator, reference period and unit before calculating an official-statistics indicator. In descriptive answers, define the measure first and then discuss uses and limitations.
4. Projection versus forecast
A projection answers a conditional question: what population would result if the stated assumptions hold? A forecast attempts to describe the most plausible future path. The distinction is important when interpreting official demographic estimates.
5. Uses and limitations
Population projections support infrastructure, education, health, pensions and labour-force planning. Their uncertainty increases with the projection horizon, and differences in assumptions can produce different results. Published projections should therefore be read with their base year, horizon and assumptions.
7. Three important questions
Try each one on your own first, then tap the answer.
Why is a population projection conditional?
Show answer
Because the projected outcome depends on explicit assumptions about fertility, mortality and migration.
A population is 50 million at the base date and is projected to grow by 2% annually for one year. Find the projected population.
Show answer
Projected population = 50 × 1.02 = 51 million.
Explain the cohort-component method used in population projections.
Show answer
Describe population by age and sex, apply survival/mortality assumptions, add births based on fertility assumptions, and incorporate migration to obtain the projected population structure.
Key takeaways
- Population projections are conditional on demographic assumptions.
- The cohort-component method works with age-sex cohorts.
- Fertility, mortality and migration are the major demographic components.
- Long-horizon projections should be interpreted with their assumptions and uncertainty.
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- Indian official statistical system: MoSPI, NSO, NSC and the data they produce
- National accounts, GDP, IIP, price indices and labour statistics
- NSS surveys, sampling designs and data quality concepts
- Written specially for the ISS exam, and useful for other government and private sector statistical exams
- Concept-focused notes to revise quickly before the exam
Official Statistics for ISS and other Government & Private Sector Statistical Examinations