The Spatial Diffusion of Fertility: A Cross-Sectional Analysis of Counties in the American South, 1940

In recent years, the diffusion perspective on variation and change in fertility levels has attracted increasing interest. Yet, few researchers have attempted to estimate the effect of diffusion on geographic variations in fertility. I employ a spatial-diffusion model to assess the effect of diffusion in shaping fertility variation across 1,052 counties in the American South in 1940. Variation in fertility levels and the "fertility potential" for each county are measured. Fertility potential is a spatial-effects variable that summarizes each county's geographic proximity to the influence of other high- or low-fertility counties. A two-stage least squares technique described by Land and Deane (1992) is used to assess the effect of fertility potential on observed fertility levels. A significant diffusion effect is inferred. The diffusion effect withstands the introduction of control variables measuring a variety of other characteristics of southern counties, many of which, themselves, have significant effects on actual fertility levels. I conclude that inter-county variation in fertility in the South was shaped by a mix of social forces, especially structural and diffusion processes.