Temporal and Regional Variations in the Seasonality of Births in Åland (Finland), 1653-1950

Monthly numbers of births are influenced by the length of the month and, thus, rates per day should be used. Comparisons of seasonality in data sets of different sizes must be based on standardized indices. Although strong seasonality exists, a poor model may incorrectly yield low seasonality measur...

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Bibliographic Details
Published in:Biodemography and social biology 2009-01, Vol.55 (1), p.103-112
Main Authors: Fellman, Johan, Eriksson, Aldur W.
Format: Article
Language:English
Subjects:
Analysis of Variance
Birth
Birth Rate - trends
Confidence Intervals
Finland
Geography
History, 17th Century
History, 18th Century
History, 19th Century
History, 20th Century
Humans
Seasons
Sweden
Time Factors
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Summary:Monthly numbers of births are influenced by the length of the month and, thus, rates per day should be used. Comparisons of seasonality in data sets of different sizes must be based on standardized indices. Although strong seasonality exists, a poor model may incorrectly yield low seasonality measures. The standard deviation of the inter-monthly variation in the indices has been used as a seasonality measure. We introduce a new measure based on analysis of variance (ANOVA). Our methods are applied on 107,896 births in the archipelago of Åland (Finland), 1653-1950. For all subregions, the birth indices for the period 1653-1850 showed marked peaks in March to April and in September to October. The seasonality is weakest for the Main Island and strongest for the most isolated parish, Kökar, which has many local/extreme socioeconomics and genetic characteristics. For the period 1851-1950, the seasonality disappeared almost totally. The variation in the seasonality between subregions can mainly be explained by socioeconomic differences, and the temporal decrease in all regions seems to be connected to diminishing differences in living conditions. Comparisons with data from Sweden and Finland show higher seasonality in Åland.
ISSN:1948-5565
1948-5573
DOI:10.1080/19485560903054788