How is world population calculated? And how accurate is the number? Is it possible that the number can be entirely wrong?
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In general, information about the world population is aggregated from information about each country’s population. From there, each country usually either conducts regular censuses or has some form of national registration to track people (or both) as it’s a very important part of running a government.
These estimates are only updated so often though (IE, the US conduct it’s census only every 10 years), so there is a little math done to the number to get the current estimate. There are three big factors that matter when creating that current estimate: Mortality rate, Birth rate, and Migration. The first obviously creates downward pressure on the number, the second upward, and the third can be either depending on if the new flow is out of or into the nation.
How accurate is it? Well, the UN is one of the better sources, and they estimate their margin of error to within 1% or so for the entire world. It varies HIGHLY depending on the country though, with less developed nations and especially wartorn nations being incredibly difficult to estimate due to difficulties in conducting censuses, and highly developed nations being very accurate. Broadly speaking, you can trust the numbers though and there is very little to no chance that the number can be entirely wrong, unless you are getting a number from a shady source.
How reliable would numbers from countries like China or North Korea? Do we actually get a number from NK?
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I always wonder how they count animal populations, especially small ones like ants. There’s no census, and who’s out there counting?
The truth is, we actually don’t know how accurate the estimate is because we’d have to know the near exact number in a sufficiently large representative area to compare it with the estimate. My guess is it can be several percentage points off, though certain undercounts (mentioned by others) can potentially be compensated by the folks with multiple citizenships that presumably are reported by each home country.
Well we have a formula/regression to calculate world population and every country has a set of statistics (the data for which is collected via national census) regarding population, mortality rate, birth rate, child mortality rate etc. These statistics are compiled and plugged into said formula and we get a world population number including the number of deaths and births per year. Although this number is fairly accurate in representing the statistical significance, when it comes to running a regression, there is room for error which is captured via an error term, this allows for a certain degree of variance shift. It’s a fairly accurate estimate. But, there are probably more people who slip out of the census then are a part of it so, there are probably more people then we estimate there are, not less.
Regarding accuracy, population numbers are often at least as accurate as they need to be. For a family of 5 getting a non-exact value is a significant error, however, for a population of 1 million then getting an estimate wrong by 100 will most likely not change the decisions made based on said population estimate.
Normally on these things what you are after is a trend. A certain number is not that relevant, just to have a ballpark will give enough information so humans can take decisions based on it. I hardly doub0t it is completely wrong, but trying to be more exact won’t provide much more relevant information for humans to make better decisions.
One thing not mentioned is that a lot of developing countries have a huge incentive to over-report their populations because the foreign aid they receive from more wealthy countries is linked to population. And, frankly, I’m not sure I trust the UN to do more than repeat what their member states say. So it depends on the source for the number. If it comes from the UN, you have this problem. If it comes from somewhere using formulas like the logistic differential equation mentioned here, it’s based on a guess of fertility rates that we don’t know is right. They all mostly agree, but their only source of ground truth is each other, so they could be agreeing with each other but not agreeing with reality. The estimates are probably mostly right, but probably off by more than their reported margins of error would have you believe.
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