Melissa McGonnell, Matt Orr, Joan Backman, Shannon A Johnson, Fiona Davidson, Penny Corkum
Examining the role of the visuospatial sketchpad in children's math calculation skills using Baddeley and Hitch's model of working memory
Acta psychologica
twin studies provide estimates genetic environmental contributions cognitive ability differences could based biased samples report wholepopulation estimates using twins unique mental surveys scotland scottish mental surveys 1st june 1932 sms1932 4th june 1947 sms1947 respectively administered validated verbal reasoning test almost everyone born 1921 1936 attending school scotland 572 twin pairs sms1932 517 pairs sms1947 information zygosity unavailable novel application mixture distribution used estimate genetic environmental components verbal reasoning variation maximum likelihood found consistent heritability approximately 070 shared environment approximately 021 estimates estimates change substantially additional quantitative traits height weight added multivariate analysis generally studies genetics methodological innovation developed implies large national data collections provide sufficient information twin pairs estimate genetic parameters even without zygosity