There's something happening here and what it is ain't exactly clear.
- Steven Stills

Previous population accounts for 98% of the variance in a nation's population change between 1950 and 2005. Life expectancy - mostly do to infant mortality accounts for another 1%. All other factors combined make up the remaining 1% and none of them is statistically significant.

But we know there is more going on than that. Developed nations with good health care, plentiful food, quality shelter, high paying jobs, and an educated population have very low birth rates. Their population increases by immigration as well as reproduction. In poor nations people reproduce faster and have more offspring, but fewer of them survive. A lack of wealth drives people from poor nations to wealthier ones.

But does that explain why the population of every nation on earth has been growing at nearly the exact same rate for the past 55 years regardless of vastly differing social, political and economic circumstances? Stay tuned!

You may be wondering about the nations in the center of the graph who's population exceeds the 95% prediction interval. Those are the oil producing nations of the Middle East. Each has had a higher than usual immigration rate due to the wealth of the local people and need for workers in the petroleum industry.

The three countries which fall below the 95% prediction interval are small island nations with limited resources. They range in populationfor 132 to 4320.