Abstract
References
1.
Case
R A M
Hosker
M E
McDonald
D B
Pearson
J T
. (1954 ) Brit. J. industr. Med.
11 , 75 .
2.
Hutchison
G
Shapiro
S
. (1968 ) Canad. J. industr. Med.
41 , 665 .
3.
Macgregor
E
Fraser
M
Mann
E F
. (1971 ) Lancet
i , 74 .
4.
Wilson
M
Chamberlain
J
Cochrane
A L
. (1971 ) Lancet
i , 297 .