Forecasting population growth is very challenging, but really important for government service provision planning and budgeting. In this post, we assess how much Statistics South Africa has revised provincial and national population estimates and how aligned their projections have been to subsequent estimates of population.
Historical ‘real-time’ (i.e. as published at different points in time) vintages of population estimates are available from 2013 from Statistics South Africa. The first two charts compare historical estimates for different years to the latest set of historical estimates. If a value is positive, it implies that historical estimates have under-estimated population. For half of the provinces, historical population estimates are now higher than they were in 2013. For the other half, estimates for 2002 to 2009 have been lowered relative to estimates from 2013. Revisions to current year estimates vary a lot across time and provinces, but have been quite large at times, ranging between -6 and 4 percentage points.
Statistics South Africa began publishing population projections in 2016, so we compare the revisions to specific year data for which forecasts are available across forecast vintages in the third chart. For the Northern Cape, Eastern Cape and Western Cape, the most recent population estimates have been higher than historical forecast, while they have been lower for the other provinces (putting 2019 and 2020 aside for Gauteng) and the national population.
Five year ahead forecast errors published in 2016 and 2017, were 0.1 and -0.9 percentage points, respectively.