Birth variations in populations which practise family planning

Area of Science:

• Demography
• Population Dynamics
• Fertility Studies

Background:

• Population models can exhibit complex dynamics, including periodicities, influenced by fertility patterns.
• Understanding fertility behavior across different birth cohorts is crucial for accurate population projections.
• Previous assumptions about the speed of achieving stable age distribution may need revision.

Purpose of the Study:

• To demonstrate the emergence of permanent periodicities in populations with multi-age fertility.
• To analyze the long-term attainment of stable age distribution after periodicity disappearance.
• To examine Swedish female fertility patterns across cohorts and periods, explaining observed fertility rate variations.

Main Methods:

• Mathematical modeling to illustrate population periodicities and stable age distribution dynamics.
• Analysis of Swedish historical demographic data, focusing on female fertility for single-year cohorts and periods.
• Calculation of total fertility rates to assess cohort reproductive replacement.

Main Results:

• Permanent periodicities can arise in populations with fertility at two or more distinct age groups.
• The disappearance of periodicity and attainment of stable age distribution can be a prolonged process.
• Swedish cohort fertility has varied significantly, particularly in birth timing, explaining irregular period fertility rates.
• Cohort fertility rates show a more regular pattern, with an increase after a low point around 1905, largely due to rising nuptiality.
• Cohorts born after approximately 1885 have not achieved self-reproduction, with a significant deficit for those born between 1895 and 1920.

Conclusions:

• Fertility patterns at multiple ages can lead to persistent population periodicities.
• Demographic transitions and fertility behaviors significantly impact population age structures over extended periods.
• Swedish cohort analysis highlights the importance of birth timing and nuptiality in fertility trends and underscores a long-term reproductive deficit in recent cohorts.