The reliability of population projections rests on the quality of the pool of data and of the assumptions on the future development of demographic parameters, i.e. mortality, birth rates and net migration. The assumptions include both values based on experience and current developments, which are often difficult to confidently categorize as trends or one-off blips at the time the projection is made. The population forecasts of the Federal Statistical Office of Germany (Statistisches Bundesamt) show that the predictive accuracy of birth rates and life expectancy has improved over the last few decades as the development in these two parameters has become more stable, whereas net migration has been virtually impossible to predict given its volatility in the past.