Temporal Differences in the Regional Twinning Rates in Sweden after 1750

Fellman, Johan; Eriksson, Aldur W.

doi:10.1375/136905203765693834

Cited by 22 publications

(36 citation statements)

References 21 publications

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“…This figure confirms that the high TWR in Gotland (21.67 per 1,000) is an outlier. This finding supports our earlier results that the TWR values for Gotland are continuously quite high (Fellman & Eriksson, 2003, 2005, 2009). Among the other counties, no outliers were found.…”

Section: Resultssupporting

confidence: 93%

“…The TWR of the county of Gotland is so extreme that it can be considered an outlier. These regional variations support the findings in Fellman and Eriksson (2003, 2005, 2009). Spatial models for TWR and especially for SR yield rather poor fit.…”

Section: Resultssupporting

confidence: 90%

“…The TWRs in Sweden are among the highest noted in Caucasian populations (cf. Fellman & Eriksson, 2003, 2005, 2009). In this study we continue the regional studies of the TWR in Fellman and Eriksson (2009) in order to identify demographic factors influencing the regional heterogeneity in the twinning rate.…”

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confidence: 99%

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Effect of Fertility on Secondary Sex Ratio and Twinning Rate in Sweden, 1749–1870

Fellman

Eriksson

2014

Twin Res Hum Genet

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We analyzed the effect of total fertility rate (TFR) and crude birth rate (CBR) on the number of males per 100 females at birth, also called the secondary sex ratio (SR), and on the twinning rate (TWR). Earlier studies have noted regional variations in 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. Here, we analyzed historical demographic data and their regional variations between counties in Sweden. We built spatial models for the TFR in 1860 and the CBR in 1751-1870, and as regressors we used geographical coordinates for the provincial capitals of the counties. For both variables, we obtained significant spatial variations, albeit of different patterns and power. The SR among the live-born in 1749-1869 and the TWR in 1751-1860 showed slight spatial variations. The influence of CBR and TFR on the SR and TWR was examined and statistical significant effects were found.

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Section: Resultssupporting

confidence: 93%

Section: Resultssupporting

confidence: 90%

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Effect of Fertility on Secondary Sex Ratio and Twinning Rate in Sweden, 1749–1870

Fellman

Eriksson

2014

Twin Res Hum Genet

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“…As examples of these factors, maternal age and birth order may be indicated (Fellman & Eriksson, 1987). However, according to Eriksson et al (1995), Eriksson and Fellman (2004), and Fellman and Eriksson (2003), such variability cannot be explained satisfactorily. Other demographic variables, including increasing population movements and urbanization processes, should be taken into account (Eriksson & Fellman, 2004; Fellman & Eriksson, 1990).…”

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confidence: 99%

A Study of Multiple Deliveries in Portugal: Indications of an Iberian Peninsula Pattern

et al. 2013

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Information on multiple deliveries with regard to Portugal is scarce. Based on data provided by the Portuguese Institute of Statistics (INE), the rates for double and triple deliveries were calculated since 1930. The results obtained show for twins a uniform temporal pattern up to the 1970s. At this time rates decreased, but later they gradually recovered, reaching their maximum level in 2010. For triplets, the highest rates occurred between 1999 and 2002. For the period 1988–2011, the rates of multiple deliveries were related to a set of variables recorded in the INE database on live births. Significant differences (p < .001) between simple and multiple deliveries were obtained for maternal age, parity and marital status. Considering the year when the delivery occurred, significant differences (p < .001) persisted for maternal age regardless of the year. For the type of mating, significance was consistently found since the year 2002 (either by using the marital or the cohabitation criteria), and for parity since 2003. With regard to territorial variation, throughout seven periods between 1930 and 2011, the rates among the 20 administrative Portuguese territories, including the two insular districts of Açores and Madeira, were mostly stable for twinning rates, with a minimum level in 1970–1989. Regarding triplets, the greatest inter-district variation was found after 1980. The results of the Portuguese study on multiple deliveries are interpreted in the context of the Iberian Peninsula based on findings reported for Spain.

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“…In this study, we consider isolates in Finland (Åland Islands), Sweden (island of Gotland and county of Älvsborg), and Norway (mountain villages). The Finnish study is based on Eriksson (1973), the Swedish study on Fellman and Eriksson (2003, 2005b, 2009), and the Norwegian study on Bonnevie and Sverdrup (1926). In our statistical analyses, we paid special attention to: (a) the robustness of the variance formula of the TWR, and (b) the most precise confidence intervals for the TWRs.…”

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confidence: 99%

Twinning Rates in Isolates

Fellman

2016

Twin Res Hum Genet

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The aim of this study was to investigate the twinning rates (TWRs) in isolates relative to the TWRs in the surrounding populations. It is not uncommon that the TWR shows extreme values (high or low rates) within isolated subpopulations. Starting from the isolated populations of the Åland Islands in Finland (high rates), we enlarged our studies to other isolated subpopulations in other countries: the island of Gotland (high rates), the county of Älvsborg located in the southwestern part of Sweden (low rates), and mountain villages in Norway. In our statistical analyses, we paid special attention to the robustness of the variance formula of the TWR and to alternative confidence intervals for the TWR. Particularly, we show how to obtain the most precise confidence intervals for the twinning rates. These statistical methods are crucial when the extreme TWRs within subpopulations are compared with the TWRs within the general population. One must decide whether the differences are real or caused by random fluctuations within the small isolates.

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Temporal Differences in the Regional Twinning Rates in Sweden after 1750

Cited by 22 publications

References 21 publications

Effect of Fertility on Secondary Sex Ratio and Twinning Rate in Sweden, 1749–1870

Effect of Fertility on Secondary Sex Ratio and Twinning Rate in Sweden, 1749–1870

A Study of Multiple Deliveries in Portugal: Indications of an Iberian Peninsula Pattern

Twinning Rates in Isolates

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