Biological and Cultural Causes of Seasonality of Deaths in Historical Populations From Poland.

Seasonal fluctuations in mortality and their causes in the nineteenth century Polish rural populations: wealthy, agriculturally and economically advanced populations from Wielkopolska, and poor populations from Silesia and Galicia (southern Poland) were described. Data-sources included parish death registers from the Roman Catholic parish of Dziekanowice in the region of Wielkopolska, Prussian statistical yearbooks for the Pozna Province as well as information from previous publications regarding Silesia and Galicia. The 19th century patterns were compared with those in present-day Poland. The occurrence of seasonality of deaths was assessed with: the Chi-squared test, the Kolmogorov-Smirnov test, and the Autoregressive Integrated Moving Average Models (ARIMA). In all populations there was a winter maximum of the number of deaths, while the minimum occurred in early summer. In the poor populations of Silesia and Galicia another statistically significant increase in the incidence of deaths was observed in the early spring. In the rich and modern villages of Wielkopolska there was no spring increase in the number of deaths, however, in all populations of Wielkopolska, irrespective of a particular pattern, a secondary mortality peak occurred in the late summer and autumn. Statistical tests used in this study did not show any clear differences in the distribution of the seasonality of deaths between the populations of Wielkopolska on the one hand, and the populations from Galicia and Silesia, on the other hand. The statistical significance of differences was, however, evident between populations representing the two distinguished by secondary peaks death seasonality patterns. Seasonal death increase split the populations under study into two groups according to the criterion of wealth.