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correlation which ascertains the degree of correlation between three variables when one of
them is held statistically constant in all the boroughs. The results of this calculation are
as shown below:
Partial correlation coefficients between standardised mortality ratios
for bronchitis and:
Male Female
Percentage in social classes IV and V when percentage
born in London is held constant +0.469 +0.185
Percentage born in London when percentage in social
classes IV and V is held constant +0.642 +0.682
For the first the coefficient for males is significant (P<.02) but the value for females
(0.185) is not: with the second the coefficients are highly significant for both males and
females (P<.001). This means that percentage born in London is more important than
social class in relation to mortality from bronchitis—a conclusion which accords with
the remark made in appendix B to my report for 1956 (page 209) dealing with atmospheric
pollution that' There is little doubt that living in London for a long period increases
the risk of dying from respiratory disease, particularly bronchitis
B
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