Unequal Years with Kin: Skewed Distributions of Lifetime Kin Overlap

Sha Jiang , Max Planck Institute for Demographic Research

Lifetime kin overlap (LKO) measures the total years an individual coexists with kin (e.g., parents or children) over the entire life course. This longitudinal measure is a critical proxy for cumulative family support potential, moving beyond the limitations of cross-sectional measures. We recover the full LKO distribution for parent, child, and joint overlaps using U.S. mortality and fertility schedules. This framework, relying only on age-specific demographic rates, is broadly applicable to any population worldwide. We compare results from a novel, efficient Fast Fourier Transform (FFT)-based convolution to those from the moments of the Markov Chain with Rewards (MCWR), a standard tool in formal demography. The FFT method accurately captures the full distributional skewness, particularly the mass at zero, which MCWR-based moment reconstructions smooth out. Applying this robust FFT method, we show that the LKO distributions in the U.S. are skewed, especially at earlier years, revealing profound inequality in access to family time, with a critical minority experiencing only 0 or 1 year of overlap. Analysis of trends from 1933 to 2021 shows that extremely short overlap (LKO < 2 years) with parents has become rare (e.g., 7% to 1% for males) due to improved survival. Similarly, short overlap with children decreases while remaining a persistent feature (e.g., 12.5% to 2.5% for males), driven structurally by lifetime childlessness. Crucially, the short duration of joint overlap is predominantly determined by the child side. Reporting the full LKO distribution is therefore essential to reveal these hidden inequalities in family support exposure, allowing for the targeting of the most vulnerable subpopulations.

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 Presented in Session 90. Kin Availability and Complex Networks in Ageing Populations