Seasonality of birth: two findings from the decennial census

The enigmatic seasonality of births in the US has been analyzed extensively, but gaps in the knowledge of this phenomenon exist along dimensions not accessed by the national vital registration system. Live births in the US have for some time followed a pattern of spring trough and summer peak--at least since the initiation of the national birth registration system in 1933. The pattern is known to be more pronounced for the South than for other regions and for blacks than for whites. In this study it has been shown that this pattern existed as far back as the 1890's, and currently is more pronounced for lower than for higher socioeconomic groups. These findings come from an analysis of census population data, rather than vital registration data. In this way census data have been used in an innovative way to address 2 aspects of the phenomenon which had heretofore not been adequately treated.