Consanguinity studies in Wisconsin I: secular trends in consanguineous marriage, 1843-1981.

Over 920,000 Roman Catholic marriages have taken place since the Archdiocese of Milwaukee was established in 1843. Most of these records are extant, and all have been examined to ascertain consanguineous marriages. The changing average population coefficient of consanguinity has been calculated, by year and by decade, showing a clear downward trend since the turn of the century. The data are compared with reports of consanguineous marriage incidence from around the world, and in particular with all available previous reports from the United States.