Abstract

References
1.
Knox
E G
, (1970 ) Developmental Medicine and Child Neurology
12 , 167
2.
Knox
E G
, (1972 ) British Journal of Preventive and Social Medicine
26 , 219
3.
Magee
P N
Schoental
R
, (1969 ) British Medical Bulletin
20 , 102
4.
Yen
S
MacMahon
B
, (1968 ) Lancet
ii , 623
