In Norway specified information of marriages between second cousins and closer relations has been recorded in the marriage certificates since January 1889. In addition, information was collected in the 1891 census and in the Medical Registration of Births (established in 1967). A ratio of second- to first-cousin marriages equal to or greater than 2 has been taken as some evidence indicating reliability of the source of data. Using this criterion, the information in the Medical Registration of Births seems most reliable, and that in the 1891 census possibly of similar accuracy. On the other hand, from 1890 the marriage certificates are unreliable with regard to the proportion of second-cousin marriages (ratio less than 1), and with regard to the proportion of first-cousin marriages from 1919. The present inbreeding in Norway is low (alpha4 = 0-000242), approximately one-eighth of the estimated level according to the 1891 census. The greatest reduction in inbreeding probably occurred after 1920.
自1889年1月起，挪威结婚证书中记录了二级表亲及更近亲属之间婚姻的特定信息。此外，在1891年人口普查和出生医学登记（1967年设立）中也收集了相关信息。二级表亲婚姻与一级表亲婚姻的比例等于或大于2，被视为数据来源可靠性的一些证据。根据这一标准，出生医学登记中的信息似乎最可靠，1891年人口普查中的信息可能具有类似的准确性。另一方面，自1890年起，结婚证书在二级表亲婚姻比例（比例小于1）以及1919年之后的一级表亲婚姻比例方面不可靠。挪威目前的近亲繁殖率较低（α4 = 0.00024），约为根据1891年人口普查估计水平的八分之一。近亲繁殖率的最大降幅可能发生在1920年之后。
