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      Temporal and Spatial Variations in the Twinning Rate in Norway.

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          Abstract

          Strong geographical variations have been noted in the twinning rate (TWR). In general, the rate is high among people of African origin, intermediate among Europeans, and low among most Asiatic populations. In Europe, there tends to be a south-north cline, with a progressive increase in the TWR from south to north and a minimum around the Basque provinces. The highest TWRs in Europe have been found among the Nordic populations. Furthermore, within larger populations, small isolated subpopulations have been identified to have extreme, mainly high, TWRs. In the study of the temporal variation of the TWR in Norway, we consider the period from 1900 to 2014. The regional variation of the TWR in Norway is analyzed for the different counties for two periods, 1916-1926 and 1960-1988. Heterogeneity between the regional TWRs in Norway during 1916-1926 was found, but the goodness of fit for the alternative spatial models was only slight. The optimal regression model for the TWR in Norway has the longitude and its square as regressors. According to this model, the spatial variation is distributed in a west-east direction. For 1960-1988, no significant regional variation was observed. One may expect that the environmental and genetic differences between the counties in Norway have disappeared and that the regional TWRs have converged towards a common low level.

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          Author and article information

          Journal
          Twin Res Hum Genet
          Twin research and human genetics : the official journal of the International Society for Twin Studies
          Cambridge University Press (CUP)
          1832-4274
          1832-4274
          August 2016
          : 19
          : 4
          Affiliations
          [1 ] Hanken School of Economics,Helsinki,Finland.
          Article
          S1832427416000499
          10.1017/thg.2016.49
          27339822
          f6d65269-fa3b-4645-a11c-81909e1d5732
          History

          assisted reproductive technology,geographical co-ordinates,county,regression analysis,multicollinearity

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