Cykliczność zmian liczby urodzeń na przykładzie wybranych krajów

In long time series of economic variables, regular trends as well as cyclical fluctuations can be observed. Similar components of long-term changes might be distinguished for demographic processes. This article aims to identify cyclical fluctuations in long-term changes of the number of births in 31 countries. The data come from the Human Mortality Database, and the time series consist of between 48 and 259 observations. In this study, a modified procedure to determine cyclical features of long-term time series was applied, which resulted in identifying turning points, phases of contraction and expansion, amplitude of phases, duration of phases and intensity of changes, and duration of cycles for each country. Comparative analysis of different characteristics of cyclical fluctuations made it possible to determine main features of long-term changes in the number of births, similarities and differences of cycles across groups of countries, and the sub-periods distinguished. The expansion phase was found to usually last longer, and its intensity to be weaker, as compared with the contraction phase. In the 20th century, especially after the Second World War, it was found that the countries under study were becoming increasingly similar in terms of the timing of turning points in the trends of birth numbers