Statisticians at the University of Washington have developed the first model for projecting population that factors in the vagaries of migration, a slippery issue that has bedeviled demographers for decades.
Their work, published online this week in the Proceedings of the National Academy of Sciences, also provides population projections for all countries worldwide—and challenges the existing predictions for some, particularly the United States and Germany.
«It turns out that for quite a few countries, migration is the single biggest source of uncertainty for population projections,» said principal investigator Adrian Raftery, a UW professor of statistics and sociology.
For the first time, the researchers used a «probabilistic» model that draws on migration rates in each country and worldwide over the past 65 years, along with patterns of fertility and mortality, to project population around the world. The findings were most striking for Germany, whose bureau of statistics has called population decline «inevitable» as the country’s populace ages.