How does the world population clock tick?

In September 2017, the United Nations Population Division (UNPD) announced the world population had reached 7.5 billion people. Whichever way you look at it, that’s a lot of bodies. But how do they come up with this number?

The figure, of course, is an estimate—there’s no way to know exact numbers down to the individual person. But surprisingly, despite all the countries in the world and all the chaos, it’s remarkably accurate.

The ever-changing total is composed by collecting, analysing and processing huge amounts of big data.

Population estimates by the UNDP rely on assessing the fertility, mortality and migration information collected from a wide range of sources. These include, but are not limited to, official birth and death records, government censuses, the World Health Organization (WHO), UNICEF, academic studies and independent health and demographic surveys.

These figures aren’t always 100 per cent accurate. Census data for example can be inaccurate to within 2 or 3 per cent (which may not sound like much, but can result in errors of tens of millions of persons), or may not be collected at all due to war or government instability.

However, by using such a wide range of data sources (including information collected on the prevalence of disease such as HIV/AIDS), and complex computational algorithms, researchers can establish a series of data points from which they can draw their conclusions. It’s never a simple straight line, but it does enable them to make predictions and project future numbers. Country and world population growth curves are revised at five-year intervals based on new collected data.

And while watching the world population clock online is interesting (if a little unsettling), it doesn’t actually tick over every time a person is added. The clock takes all the information available to determine population increase over the course of the coming year. Because population growth is continuous, and a clock that updates once every 12 months is a little boring, it divides the estimated annual increase by the number of seconds in a year (31 536 000). This gives it the appearance of constantly ticking upwards.