1. 1 Motivation and main question of this research A modern society faces two alternatives with regards to its population trend. It can either grow or age. A population which chooses not to grow any more (or which chooses to shrink) will necessarily age. And because of the impossibility of all populations in all countries growing forever, it is likely that every country will face this ageing process at some point in time. Because of this and the importance of economic growth for the well-being of a society, the relationship between an ageing population and economic growth will be relevant for each country. It is already an important and much discussed matter for many. Although population ageing is faced by virtually all industrialised countries, the time frame and the intensity of the process vary. The substantial changes forecasted for the demographic structure of many countries over coming decades have led to substantial research activity aiming to analyse and quantify the effects of these changes on a nation's economic performance. sub A change in population size and population growth rate can af­ fect both the demand and supply side of an economy. The extent of the effects, however, is not clear. sub The structure of a population (for example, regarding distribution of age or gender) may also influence the economic performance of a society.