Sibship size and height before, during, and after the fertility decline

Background: There is still much to learn about the explanation for the often-found negative association between sibship size and different child outcomes. A plausible explanation is resource competition between siblings in larger families, as suggested by the resource dilution hypothesis. Objective: This study contributes to our understanding of these mechanisms by investigating the association between sibship size and height before, during, and after the fertility decline to test predictions based on the resource dilution hypothesis. Methods: The investigation is conducted using information from universal conscript inspections linked to a longitudinal demographic database. Regression analyses estimate a model derived from the resource dilution explanation and analyze the association between sibship size and height among men born in 1821-1950 in southern Sweden. Results: The results show that the association between sibship size and height was negative from the mid-nineteenth century until the mid-twentieth century. There is no association in the early nineteenth century. The strength of the association is gradually weakened over time for men born from the 1840s until the 1940s. It is most consistent among men born from 1881-1921, corresponding closely to the time for the fertility decline in the area. The association is not a result of confounding by observable demographic or socioeconomic differences between families. Conclusions: The results are in line with resource dilution being an important explanation for the negative association between sibship size and height. Resource dilution in larger families still seems to be dependent on the societal and historical context.