Reading a population pyramid

Demography also studies what a population is made of: age, gender, work, education. This is called population composition.

One key measure is the sex ratio: the number of females for every 1,000 males. It shows the balance between men and women, and tells us about a country's social, economic and cultural life.

India's sex ratio was 933 in the 2001 Census, and improved to 943 in 2011. Women were 48.5 per cent of the population.

Both numbers are well below 1,000. But Kerala, Puducherry and Tamil Nadu were at or near 1,000, or above. (What might the reasons be? The book asks you to think about it.)

A balanced sex ratio matters for fair development, a stable society and steady population growth.

A population pyramid (population structure diagram) is a special graph. It shows how many people there are in each age group, split into males and females:

• the bottom shows young people (children and teenagers);
• the middle shows adults;
• the top shows old people.

Its shape tells the story:

• wide base → many children being born; a young, growing population (like India or Nigeria);
• widest in the middle → mostly working adults; a stable population;
• wide top → more old people than young adults; an ageing population (like Japan).

In the 1950s, India's pyramid was a narrow triangle: lots of children, few old people, a high birth rate, and life expectancy of only about 30–35 years.

Today it looks less like a triangle and more like a bell:

• the base is narrower: families have fewer children;
• the middle is much wider: a huge number of people aged 15 to 60. This is India's demographic dividend;
• the top is slowly widening: people are living longer.

So India has moved from a young, fast-growing population to a more balanced one. Slowly, it may begin to age, as Japan and China already are.