1. Congenital malformations of the central nervous system;Bradshaw;Popul Trends,1980
2. Tests for linear trends in proportions and frequencies;Armitage;Biometrics,1955
3. Possible prevention of neural tube defects by periconceptional vitamin supplementation;Smithells;Lancet,1980
4. Unrecognised epidemic of anencephaly and spina bifida;McMahon;Lancet,1971
5. Anencephalus, spina bifida and congenital hydrocephalus: England and Wales 1964-1972;Rogers;Stud Med Popul Subj,1976