Describe the population pyramid and the age structure of a population.

Population Pyramid and Age Structure

• The three classical shapes:
• The triangular or expansive pyramid — a broad base narrowing rapidly upward, indicating high birth rate and high death rate, a young population and rapid growth; typical of a country in early transition
• The bell-shaped or constrictive pyramid — with a narrowing base, indicating a falling birth rate and an ageing population
• The urn-shaped or stationary pyramid — roughly rectangular up to old age, indicating low and stable birth and death rates, with a narrower base than middle if the population is declining
• What can BE read from A pyramid is what an examiner actually wants:
• The width of the base indicates the current birth rate — a base narrower than the group above it indicates a recently falling birth rate
• The rate of narrowing upward indicates mortality
• An indentation at a particular age group indicates a past event — a war, famine, epidemic or period of out-migration, which moves upward through the pyramid over subsequent decades as that cohort ages
• Asymmetry between the sexes indicates sex-selective mortality, migration or sex selection
• A bulge in the working ages indicates the demographic dividend period
• The INDIAN pyramid is triangular but with a narrowing base, reflecting fertility having fallen to replacement while the large cohorts born earlier move up through the reproductive ages — which is population momentum shown pictorially
• Different Indian states have visibly different pyramids at the same time, with Kerala approaching a bell and Bihar still strongly triangular
• The dependency ratio = (population under 15 plus population 65 and over) divided by population 15 to 64, expressed per 100
• It divides into the young (child) dependency ratio and the old-age dependency ratio, and the distinction matters because the two have entirely different fiscal and service implications — children need schools and immunisation, the elderly need pensions and chronic care
• Its limitation should be stated — it assumes everyone aged 15 to 64 is productive and everyone outside that range is not, which is false in a country with widespread child labour, high youth unemployment, work continuing well past 65, and large numbers of women outside recorded employment
• It is therefore a crude measure of economic burden, useful for comparison rather than as a literal statement of who supports whom
• The trajectory of the dependency ratio during the transition — it is high initially because of many children; then falls as fertility declines and those children enter working age — the dividend window; then rises again as the population ages
• India is in the falling phase now, which is the window of opportunity, and it will not remain open indefinitely
• The practical uses of age structure data for health planning — projecting the need for maternal and child services from the size of the reproductive-age and under-five groups; projecting school and immunisation requirements; anticipating the geriatric and non-communicable disease burden from the size of the cohorts now in middle age; workforce planning; and calculating age-specific rates and standardising for comparison
• The key insight is that age structure is predictable decades ahead, since everyone who will be 60 in thirty years is already alive and countable today
• Health planning for the elderly therefore requires NO forecasting of birth rates and admits of NO excuse for surprise — which is a point worth making, since ageing is repeatedly treated as though it were unexpected
• Everyone who will be sixty in thirty years is alive, which makes age structure the most predictable planning variable there is
• An indentation marks a war, famine or epidemic, and travels upward through the pyramid as that cohort ages
• A base narrower than the group above indicates a recently falling birth rate, which is what India now shows
• The dependency ratio is a crude measure, assuming everyone of working age works and nobody outside it does
• Young and old dependency differ entirely; one needs schools and immunisation, the other pensions and chronic care
• The ratio falls then rises during transition, and the falling phase is the dividend window
• Different Indian states show different pyramids at the same moment, with Kerala approaching a bell and Bihar still triangular
• Asymmetry between the sexes signals selection, differential mortality or migration, and should prompt enquiry
• Triangular means young and rapidly growing, bell means falling fertility, and urn means stationary
• Project maternal services from the reproductive age group, which is directly readable off the pyramid
• Anticipate the NCD burden from middle-aged cohorts, since those people are already counted and their trajectory is known
• The rate of narrowing upward reflects mortality, which is how a pyramid conveys two rates at once
• Momentum is what the Indian pyramid shows, with a narrowing base below large cohorts still entering reproductive age