Annual Symposium: Recent Trends in Mortality and Morbidity in Ireland: Projecting Population Mortality for Ireland
Whelan, S., Journal of the Statistical and Social Inquiry Society of Ireland
Increasing human longevity in the more advanced nations is one of the greatest social achievements over the last one-hundred and fifty years. In Ireland, life expectancy began to increase markedly from the last years of the nineteenth century. In 1900-1902, life expectancy at birth was 49.3 years for males and 49.6 years for females. The latest official Irish Life Table, reflecting the experience in the years 2001-2003, shows life expectancies to have increased to 75.1 years for Irish males and 80.3 years for females--a rate of increase averaging 0.26 years for males and 0.30 years for females with the passage of each calendar year over the 20th century.
It is of interest to ponder how life expectancies may change over the course of the 21st century. Aside from personal planning, a good estimate of longevity would aid the State in, say, designing and financing of a pension and healthcare system to better achieve sustainability and intergenerational equity. This paper reviews the different approaches to projecting mortality rates and applies a couple, using several different sets of assumptions, to help form a judgement on the course of mortality in Ireland over the 21st century. Specifically, we attempt to answer the question: how long will a child born in Ireland in 2006 live on average?
Mortality patterns have been changing in the developed world at a remarkable pace over the recent past. Mortality improvements have tended to accelerate at many ages and most especially at the older ages. The pattern is no different in Ireland. In particular, Ireland is now experiencing an average rate of mortality improvement higher than at any recorded period in the past. The actuarial profession, the profession that prices and reserves for mortality risks and generally advises on the prudent management of life offices and pension funds, has recently ceased publishing mortality tables with forecasts of mortality improvements because of the dramatic changes of late and the consequent very significant uncertainty inherent in any single projection. It is of interest to explore the possible long term affects of current emerging patterns, even if the resultant projections must inevitably be surrounded by considerable uncertainty.
The structure of the paper is as follows. First, we overview the different methods of projecting mortality rates. Second, we analyse mortality trends in Ireland over both long and short periods of time. [Appendix I critically reviews the underlying data from which the Irish mortality experience is inferred.] Third, we project mortality rates in Ireland and estimate future life expectancies, including for children born in 2006, by different methods and on different bases. This section outlines the new approach to mortality forecasting adopted in the forthcoming official projection (CSO (2008) and appendix 11 outlines the new approach in detail. Finally we conclude that children born in 2006 can reasonably be expected to live to their early nineties for males and mid-nineties for females.
2. METHODS OF PROJECTING MORTALITY
There are several different approaches to projecting mortality rates. First, one can model the ageing process and apply the model to forecast future changes. However a satisfactory model or 'law of mortality' has proved elusive, despite notable attempts by, inter alia, Gompertz (1825, 1860), Makeham (1860), Perks (1932), and Beard (1971) (see, for instance, Olshansky & Carnes (1997) or Forfar (2004) for a review). In fact, attempts to detect a simple mathematical formula that governs mortality over the whole of life are now largely abandoned. Accordingly, this ideal approach is not practical.
The study of the ageing process and how it evolves identifies two distinct mechanisms of mortality change. The first is secular change such as better nutrition, better housing, and innovations in diagnosis and treatment of life-threatening conditions. …