Demography - Taking the measure of uncertainty

Forecasts of the size of the world's population in years to come are typically given as a medium (central) estimate bracketed by high and low variants. A different approach, which is for instance used in informing decisions over financial investments, is now being brought to bear on demographic forecasting. It involves estimating a range of population sizes in the future, along with the associated probabilities that the forecast will be accurate. Using this method, the odds that the world's population will double by the year 2050 are less than a third, but it is essentially a sure thing that the fraction of the population over the age of 60 will double.