title: Burt's twins: a question of numbers.
abstract: This article estimates the number of monozygotic twins raised apart (MZA) potentially available to Cyril Burt in his twin studies. It concludes that between 77,000 and 88,000 monozygotic (MZ) twin pairs would have been born and survived to the age of ten in the relevant period in England and Wales, and that between 750 and 1,750 surviving pairs are likely to have been separated during childhood. Burt's claim to have collected 53 MZA pairs is therefore not inherently implausible. However, when all the other constraints on Burt's studies are taken into account, his numbers are problematic. There are also serious difficulties with his claim to have studied 12 pairs born to middle-class parents. It is highly improbable that Burt could have located a majority of these cases through personal contacts as he claimed.
authors.affiliation: djburbridge@aol.com
authors.forename: David
authors.initials: D
authors.lastname: Burbridge
mesh_terms: D000367:Age Factors; D001525:Behavioral Sciences / Q000266:history*; D003718:Denmark; D005387:Finland; D049673:History, 20th Century; D006801:Humans; D012042:Registries; D012106:Research / Q000592:standards*; D035781:Siblings; D012923:Social Class; D012931:Social Environment; D017741:Survivors; D013548:Sweden; D018433:Twin Studies as Topic / Q000266:history*; D014430:Twins, Monozygotic; D006113:United Kingdom; D014481:United States