The Seasonality of Births in Canada and the Provinces, 1881-1989: Theory and Analysis

Abstract

The seasonality of births and the determinants of seasonality has not been easily explained by researchers due to inadequate theories. Explanatory variables discussed are sociocultural and exogenous environmental factors and endogenous proximate determinants. The basic framework of this study employs models developed by Davis and Blake and later revised by Bongaarts and assumes environment and social structural factors which affect reproduction through intervening variables. The aim is to provide a skeletal structure of some of the causal linkages. Canadian Census and Vital Statistics data are analyzed in a time varying parameter model used by Seiver for Canada and its provinces in 1881 and 1926 to 1989. The pattern of seasonality and changes in the pattern over time are described. Hypotheses are generated as explanations of socioeconomic influences marriage patterns holidays agricultural and economic cycles temperature photoperiod and birth month preference. The dependent variable is a 12-month moving average of births. The results indicate that in 1926 births were 4833% above a centered 12-month moving average of births. In 10 years time the March effect would be reduced to 4.305%. The pattern has changed very little since 1926. The peak in births appears in March through July and rises again in September. After 1970 the peak is in September and the spring-summer period still has a high number of births. In 1881 the pattern was different from that of the mid 1920s: births peaked in March and declined in May and June. There was below-average fertility in April September and November. It was reasoned that stillbirths could not account for the differences between 1881 and 1926. Peak marriages were in June which could affect the peak of births in March but the peak in September showed a decline in births in June; thus marriage may be a partial factor. In 1881 the timing of births for the spring and summer probably reflected timing of births in order to avoid the extremes of cold; holidays could also explain this pattern. The birth troughs do not conform to the heat or photoperiod hypotheses. Preference is in a strong position to affect births. All provinces follow the national pattern with a few exceptions. The Territories show a different pattern and then a gradual change to the national pattern; modernization is given as the reason.