Q.What are the three components of population change?
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Start your 14-day free trial to unlock the full solution →Population change is driven by three components: births, deaths, and migration — the only ways a population can grow or shrink.
To understand how any population — whether of a village, a city, or a whole country — changes over time, you have to look at the three fundamental forces that add people and remove people. These are the components of population change: fertility (births), mortality (deaths), and migration (movement). No other factor can alter the size of a population. Think of it like a simple balance sheet: births and in-migration are the inflows; deaths and out-migration are the outflows. The net result — the difference between inflows and outflows — is the actual population change.
Births are the most obvious source of population increase. The number of babies born in a given period (usually a year) is called the number of live births. But raw numbers don't tell the whole story; demographers use the crude birth rate (CBR), which is the number of live births per 1,000 people in the population. This rate allows fair comparisons between places of different sizes. A high CBR means a rapidly growing population, provided death rates are low. In India, for example, the CBR has been falling steadily over the decades as families choose to have fewer children, but it remains higher than in many developed countries.
Deaths are the natural subtraction. The crude death rate (CDR) is the number of deaths per 1,000 people per year. When a population has a high CDR — due to disease, famine, or poor healthcare — it can shrink or stagnate. The great achievement of modern medicine and public health has been to drive down death rates dramatically, especially infant and child mortality. This is why even modest birth rates can still produce rapid population growth: more babies survive to adulthood, and people live longer. The difference between the birth rate and the death rate is called the natural increase (or natural decrease, if deaths exceed births).
Natural increase does not include migration. It is purely the balance of births and deaths. So a country can have a positive natural increase but still lose population if many more people emigrate than are born. …
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