Temporal variation in rates of multiple maternities in Denmark, 1850-2012

We analysed geographic variation in the number of males per 100 females at birth also called the secondary sex ratio (SR), the crude birth rate (CBR), the total fertility rate (TFR) and the twinning rate (TWR). Earlier studies have noted geographic variations in the TWR and racial differences in the SR. Statistical analyses have shown that comparisons between SRs demand large data sets
because random fluctuations in moderate data are marked. Consequently, reliable results presuppose national birth data. In this study, we analysed historical demographic data and investigated the geographic variations between the counties in Sweden for the SR among the live born (1749-1869), the CBR in 1751-1870, the TFR in 1860 and the TWR in 1751-1860. We built spatial models and as regressors we used geographic co-ordinates for the residences of the counties in Sweden. The influence of the CBR and TFR on the SR and TWR was examined. For all variables, we obtained spatial variations, albeit of different patterns and power. Hence, no common spatial pattern for the demographic variables SR, TFR, CBR and TWR was detected, but a better fit was noted for TFR, CBR and TWR than for SR.