Towards a Theory of Lowest-Low Fertility

Hans-Peter Kohler, Max Planck Institute for Demographic Research

Lowest-low fertility, defined as a period total fertility rate below 1.3, has rapidly spread in Europe during the 1990s and is likely to expand further. This paper argues that the emergence and persistence of this new phenomenon is due to the combination and interaction of four factors. First, tempo- and compositional distortions reduce the TFR below the associated level of cohort fertility, and these distortions can be quantified with appropriate adjusted measures. Second, late childbearing has become a rational response to increased returns to human capital and high economic uncertainty in early adulthood. Third, social interaction reinforces the behavioral adjustment of individuals, and it can lead to postponement transitions with large and persistent changes in the mean age at birth. Fourth, delayed childbearing is associated with postponement-quantum interactions that reduce completed fertility. The paper concludes with some speculations about future trends in lowest-low fertility countries and candidates.