Abstract
Local area population forecasts have a wide variety of uses in the public and private sectors. But not enough is known about the errors of such forecasts, particularly over the longer term (20 years or more). Understanding past errors is valuable for both forecast producers and users. This paper (i) evaluates the forecast accuracy of past local area population forecasts published by Australian State and Territory Governments over the last 30 years and (ii) illustrates the ways in which past error distributions can be employed to quantify the uncertainty of current forecasts. Population forecasts from the past 30 years were sourced from State and Territory Governments. Estimated resident populations to which the projections were compared were created for the geographical regions of the past projections. The key features of past forecast error patterns are described. Forecast errors mostly confirm earlier findings with regard to the relationship between error and length of projection horizon and population size. The paper then introduces the concept of a forecast ‘shelf life’, which indicates how far into the future a forecast is likely to remain reliable. It also illustrates how past error distributions can be used to create empirical prediction intervals for current forecasts. These two complementary measures provide a simple way of communicating the likely magnitude of error that can be expected with current local area population forecasts.
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Source New South Wales Department of Planning & Environment (2016); authors’ prediction intervals
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References
ABS. (2013). Australian demographic statistics. December quarter 2012. Catalogue No. 3101.0. Canberra: ABS.
Bell, M., Wilson, T., & Charles-Edwards, E. (2011). Australia’s population future: Probabilistic forecasts incorporating expert judgement. Geographical Research, 49(3), 261–275.
Bijak, J., Alberts, I., Alho, J., Bryant, J., Buettner, T., Falkingham, J., et al. (2015). Probabilistic population forecasts for informed decision making. Journal of Official Statistics, 31(4), 537–544.
Bongaarts, J., & Bulatao, R. A. (Eds.). (2000). Beyond six billion: Forecasting the world’s population. Washington, DC: National Academy Press.
Hyndman, R., & Khandakar, Y. (2008). Automatic time series forecasting: The forecast package for R. Journal of Statistical Software, 27(3), 1–22.
Isserman, A. M. (1977). The accuracy of population projections for subcounty areas. Journal of the American Institute of Planners, 43, 247–259.
Keilman, N. (1999). How accurate are the United Nations world population projections? In W. Lutz, J. W. Vaupel, & D. A. Ahlburg (Eds.), Frontiers of population forecasting (pp. 15–41). New York: Population Council.
Keilman, N., Pham, D. Q., & Hetland, A. (2002). Why population forecasts should be probabilistic—Illustrated by the case of Norway. Demographic Research, 6, 409–454.
Keyfitz, N. (1981). The limits of population forecasting. Population and Development Review, 7(4), 579–593.
Lee, R. (1999). Probabilistic approaches to population forecasting. In W. Lutz, J. W. Vaupel, & D. A. Ahlburg (Eds.), Frontiers of population forecasting (pp. 156–190). New York: Population Council.
Lee, R., Miller, T., & Edwards, R. D. (2003). The growth and aging of California’s population: Demographic and fiscal projections, characteristics and service needs. UC Berkeley: Center for the Economics and Demography of Aging.
Lutz, W., Sanderson, W. C., & Scherbov, S. (2004). The end of world population growth. In W. Lutz, W. C. Sanderson, & S. Scherbov (Eds.), The end of world population growth in the 21st century (pp. 17–83). London: Earthscan.
Mullainathan, S., & Spiess, J. (2017). Machine learning: An applied econometric approach. Journal of Economic Perspectives, 31(2), 87–106.
New South Wales Department of Planning & Environment. (2016). 2016 NSW population and household projections. Online at http://www.planning.nsw.gov.au/projections. Sydney: Department of Planning & Environment.
Office for National Statistics. (2008). Subnational population projections accuracy report. London: Office for National Statistics.
Office for National Statistics. (2015). Subnational population projections accuracy report. Titchfield: Office for National Statistics.
Rayer, S. (2008). Population forecast errors: A primer for planners. Journal of Planning Education and Research, 27, 417–430.
Rayer, S., & Smith, S. K. (2010). Factors affecting the accuracy of subcounty population forecasts. Journal of Planning Education and Research, 30, 147–161.
Rayer, S., & Smith, S. K. (2014). Population projections by age for Florida and its counties: Assessing accuracy and the impact of adjustments. Population Research and Policy Review, 33(5), 747–770.
Rayer, S., Smith, S. K., & Tayman, J. (2009). Empirical prediction intervals for county population forecasts. Population Research and Policy Review, 28(6), 773–793.
Rayer, S., and Wang, Y. (2015). Projections of Florida population by county, 2015–2040, with estimates for 2014. Bureau of Economic and Business Research, University of Florida.
Royston, P., & Altman, D. G. (1994). Regression using fractional polynomials of continuous covariates: parsimonious parametric modelling. Journal of the Royal Statistical Society: Series C (Applied Statistics), 43(3), 429–467.
Smith, S. K., & Rayer, S. (2011). An evaluation of population forecast errors for Florida and its counties, 1980–2010. Bureau of Economic and Business Research, University of Florida.
Smith, S., & Shahidullah, M. (1995). An evaluation of population projection errors for census tracts. Journal of the American Statistical Association, 90, 64–71.
Smith, S., & Sincich, T. (1988). Stability over time in the distribution of population forecast errors. Demography, 25, 461–474.
Smith, S. K., Tayman, J., & Swanson, D. A. (2013). A practitioner’s guide to state and local population projections. Dordrecht: Springer.
Statistics New Zealand. (2008). How accurate are population projections? An evaluation of statistics New Zealand population projections, 1991–2006. Wellington: Statistics New Zealand.
Stoto, M. A. (1983). The accuracy of population projections. Journal of the American Statistical Association, 78(381), 13–20.
Tayman, J. (2011). Assessing uncertainty in small area forecasts: State of the practice and implementation strategy. Population Research and Policy Review, 30, 781–800.
Tayman, J., Schafer, E., & Carter, L. (1998). The role of population size in the determination and prediction of population forecast errors: An evaluation using confidence intervals for subcounty areas. Population Research and Policy Review, 17, 1–20.
Tayman, J., Smith, S. K., & Rayer, S. (2011). Evaluating population forecast accuracy: A regression approach using county data. Population Research and Policy Review, 30(2), 235–262.
Tye, R. (1994). Local authority estimates and projections: How are they used and how accurate do they need to be? Working paper 9, estimating with confidence project. Department of Social Statistics, University of Southampton, UK.
Wilson, T. (2011). A review of sub-regional population projection methods. Report to the office of economic and statistical research. Queensland centre for population research, school of geography, planning and environmental management, The University of Queensland, Brisbane.
Wilson, T. (2013). Quantifying the uncertainty of regional demographic forecasts. Applied Geography, 42, 108–115.
Wilson, T. (2015). Short-term forecast error of Australian local government area population projections. Australasian Journal of Regional Studies, 21(2), 253–275.
Wilson, T., & Rowe, F. (2011). The forecast accuracy of local government area population projections: A case study of Queensland. Australasian Journal of Regional Studies, 17(2), 204–243.
Wilson, T. (2012). Forecast accuracy and uncertainty of Australian Bureau of statistics state and territory population projections. International Journal of Population Research, 2012, 12.
Yamauchi, M., Koike, S., & Kamata, K. (2017). How accurate are Japan’s official subnational projections? Comparative analysis of projections in Japan, English-speaking countries and the eu. In D. A. Swanson (Ed.), The frontiers of applied demography (pp. 305–328). Dordrecht: Springer.
Acknowledgements
This study was supported by the Australian Research Council (Discovery Project DP150103343). The authors would like to extend their thanks to the state and territory government demographers who generously supplied past projections and advice for this study.
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Wilson, T., Brokensha, H., Rowe, F. et al. Insights from the Evaluation of Past Local Area Population Forecasts. Popul Res Policy Rev 37, 137–155 (2018). https://doi.org/10.1007/s11113-017-9450-4
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DOI: https://doi.org/10.1007/s11113-017-9450-4