1. The repeat frequency of twinning;Bulmer;Ann. hum. Genet.,1958
2. Twins and congenital heart disease;Campbell;Acta Genet, med. (Roma),1961
3. Major central nervous system malformations in South Wales. I. Incidence, local variations and geographical factors;Carter;Brit. J. prev. soc. Med.,1968
4. Anencephalus and spina bifida;Carter;Brit. med. J.,1969
5. Declining incidence of central nervous system anomalies in New York State;Gittelsohn;Brit. J. prev. soc. Med.,1962