Towards a multi-modal fertility curve?

Marion Burkimsher, Independent Researcher and Université de Lausanne

The shape of the age-specific fertility rate curve is often assumed to be approximately bell-shaped. However, a bulge or shoulder in the early part of the curve has been noted in a number of countries. This study investigates the evolution of the shape of the cohort ASFR curves for all 15 countries in the Human Fertility Database, those for which birth-order-specific data are available. It was found that the development of a bi-modal distribution was widespread for first birth fertility curves, and this might be part of the normal evolution from an early to a later fertility schedule. However, for second births the transition from an earlier schedule to a later one appeared to happen with a much less pronounced development of a second mode. Possible causes of the early ‘shoulder’ are considered, and the immigrant hypothesis is considered to be unlikely. There is ample scope for further investigations into this phenomenon and several avenues are suggested.