Disagreement on whether there are 7 billion people on earth just yet

There have been a number of recent stories about how the world’s population has reached 7 billion. Interestingly, not everyone agrees that this has happened yet:

According to United Nations demographers, 6,999,999,999 other Earthlings potentially felt the same way on Monday when the world’s population topped seven billion. But if you’d rather go by the United States Census Bureau’s projections, you’ve got some breathing room. The bureau estimates that even with the world’s population increasing by 215,120 a day, it won’t reach seven billion for about four months.

How do the dueling demographic experts reconcile a difference, as of Monday, of 28 million, which is more than all the people in Saudi Arabia?

They don’t.

“No one can know the exact number of people on the globe,” Gerhard Heilig, chief of the population estimates and projections section of the United Nations Population Division, acknowledges.

Even the best individual government censuses have a margin of error of at least 1 percent, he said, which would translate in the global aggregation to “a window of uncertainty of six months before or six months after Oct. 31.” An error margin of even as little as 2 percent would mean that Monday’s estimate of seven billion actually was 56 million off (which is more people than were counted in South Africa).

Figuring this out is not an easy task. It requires a central group to tabulate results from all of the countries around the world. Could there be a difference in the reliability and validity of the results across nations? For example, can we trust population counts from honed operations in the United States and other Western nations more than counts from Third World countries? (I wish the article went into this: how accurate are population figures from different countries? How big might the margins of errors be?) I’ve seen this before when doing some research in graduate school on suicide figures that the United Nations has collected – in the period I was looking at, roughly 1950 to 1970, some countries didn’t report, some had rougher estimates, and countries could have different definitions about what constitutes a suicide. Absolute population counts should be more straight forward but I imagine there could be a number of complications.

Will we get another round of news stories when the Census Bureau says we have hit 7 billion? I wonder if the perceived global authority of the United Nations versus that of the Census Bureau plays a role. For example, did the New York Times report the 7 billion figure as front-page news and then print this caveat story later in the news section?

A final note: the story ends by suggesting the two estimates are not that far off. If we could be so lucky that all of our estimates have only a 1% margin of error, science would benefit greatly. But it is a reminder that official figures are estimates, not 100% counts of social phenomenon.

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