What will happen to the population in a few decades' time if the current economic and political developments and trends in birth rates, mortality and migration predicted by current knowledge continue? Population projections show how the composition of the population changes if certain behaviours persist. When preparing population projections, current trends are extended to the future. However, many variables need to be taken into account, such as the number of children and the age of mothers, mortality in different age groups, the age distribution of the migrating population and what changes