Lent impact on the seasonality of conceptions during the twentieth century in Spain

In European past populations, religious canons shaped the seasonal distribution of marriages and births by means of banning weddings and sexual intercourse during important holidays within the religious calendar. In contemporary secularized societies, this seasonal modeling has disappeared. A few pieces of evidence have been gathered to explain how they have disappeared. This paper analyzes the impact of Lent on the seasonality of conceptions during the last century in Spain. Data births of the entire Spanish population born in Spain and alive on the first of January 2003 (more than 39 million) containing the date, size of the municipality (six groups) are used. To analyze this seasonality, we have used time-series techniques. We have built an ad hoc temporal regressor starting from the number of days of Lent that corresponds to each month. We have also used regression models with autoregressive and moving average errors (regARIMA models) to estimate, by maximum likelihood, the set of model parameters. The paper gathers new evidences about the importance of religion on the preproduction of Spanish population until very recently. They show that during the twentieth century, in Spain, there were a significant decrease in conceptions during Lent and a significant rebound after this period. We note that this previous effect disappeared in 1975-1980, when both democracy and the contraception revolution began in Spain. After this period, the seasonality of birth in general disappears.