Table 1.

Details of data used in the present study, for each population separately and for all populations combined.

Population	Locations	Maternal birth period	Mothers	Non-twinners	Twinners	Twinner rate (‰)	Offspring birth period	Births	Singleton births	Twin births	Twinning rate (‰)	Total births (min-median-max)	References
Finland East	Jaakkima, Rautu	1742–1899	871	781	90	103.33	1771-1940	4444	4347	97	21.83	1-7-17	33,34
Finland Lapland	Inari, Enontekiö and Sodankylä	1700–1884	757	695	62	81.9	1725-1918	3548	3482	66	18.6	1-6-13	8
Finland SW-Archipelago	Hiittinen, Kustavi, Rymättylä	1709–1899	2737	2443	294	107.42	1732-1942	12136	11816	320	26.37	1-6-15	3,6
Finland West	Ikaalinen, Pulkkila, Tyrvää	1700–1899	5669	5200	469	82.73	1721-1943	30733	30224	509	16.56	1-7-16	33,34
Krummhörn	Lower Saxony, Germany	1705–1823	3739	3461	278	74.35	1725-1868	17634	17336	298	16.9	1-6-17	5
Sami Lapland	Inari, Enontekiö and Sodankylä	1703–1880	957	885	72	75.24	1729-1920	4858	4780	78	16.06	1-7-13	8,32
Sweden Lapland	Karesuando, Jukkasjärvi, Jokkmok, Vilhelmina and Jällivaara	1721–1878	1943	1797	146	75.14	1749-1902	11106	10946	160	14.41	1-8-17	32,35,36
Switzerland	Linthal, Elm	1700–1899	4617	4394	223	48.3	1720-1945	21374	21138	236	11.04	1-6-18	31
All the above	All the above	1700–1899	21290	19656	1634	76.75	1720-1945	105833	104069	1764	16.67	1-7-18	This paper